- Prime number
- A whole number greater than 1 with exactly two distinct factors: 1 and itself (2, 3, 5, 7, 11, 13...).
- Composite number
- A whole number greater than 1 that has more than two factors (4, 6, 8, 9, 10...). It is not prime.
- Is 1 prime?
- No. A prime has exactly two distinct factors; 1 has only one factor (itself), so it is neither prime nor composite.
- Is 2 prime?
- Yes. 2 is the only even prime number — every other even number is divisible by 2.
- Factor
- A whole number that divides another evenly with no remainder. Factors of 12 are 1, 2, 3, 4, 6, 12.
- Multiple
- The product of a number and any whole number. Multiples of 5 are 5, 10, 15, 20, 25...
- Greatest common factor (GCF)
- The largest factor shared by two numbers. GCF of 48 and 60 is 12. Find it by listing factors or using prime factorization.
- Least common multiple (LCM)
- The smallest multiple shared by two numbers. LCM of 8 and 12 is 24. Useful for adding fractions and 'when do events line up again' problems.
- Prime factorization
- Writing a number as a product of primes. 60 = 2 × 2 × 3 × 5 = 2² × 3 × 5.
- Number of factors of a product of two distinct primes
- Exactly 4. If x and y are distinct primes, xy has factors 1, x, y, and xy.
- Integer
- A whole number and its opposite, including zero: ..., −2, −1, 0, 1, 2, ... No fractions or decimals.
- Rational number
- Any number that can be written as a fraction a/b where a and b are integers and b ≠ 0. Includes terminating and repeating decimals.
- Irrational number
- A number that cannot be written as a fraction; its decimal never ends and never repeats. Examples: √2, π.
- Absolute value
- The distance of a number from zero on the number line; always nonnegative. |−7| = 7 and |7| = 7.
- Order of operations (PEMDAS)
- Parentheses, Exponents, Multiplication/Division (left to right), Addition/Subtraction (left to right).
- Adding fractions
- Find a common denominator, rewrite each fraction, add the numerators, keep the denominator, then simplify. 3/4 + 5/6 = 9/12 + 10/12 = 19/12.
- Subtracting fractions
- Use a common denominator, subtract numerators, keep the denominator, simplify. 11/12 − 1/4 = 11/12 − 3/12 = 8/12 = 2/3.
- Multiplying fractions
- Multiply numerators and multiply denominators, then simplify. 2/3 × 9/10 = 18/30 = 3/5.
- Dividing fractions
- Multiply by the reciprocal of the second fraction (keep–change–flip). 3/4 ÷ 2/5 = 3/4 × 5/2 = 15/8.
- Reciprocal
- The multiplicative inverse — flip the fraction. The reciprocal of 2/5 is 5/2; the reciprocal of 4 is 1/4. A number times its reciprocal equals 1.
- Simplifying a fraction
- Divide the numerator and denominator by their GCF. 18/30 ÷ 6/6 = 3/5.
- Improper fraction
- A fraction whose numerator is greater than or equal to its denominator, such as 7/4. It can be written as the mixed number 1¾.
- Mixed number
- A whole number plus a fraction, such as 2½. Convert to an improper fraction by multiplying the whole number by the denominator and adding the numerator: 2½ = 5/2.
- Fraction to decimal
- Divide the numerator by the denominator. 3/4 = 3 ÷ 4 = 0.75.
- Decimal to fraction
- Write the decimal over its place value, then simplify. 0.75 = 75/100 = 3/4.
- Percent to decimal
- Divide by 100 (move the decimal two places left). 45% = 0.45.
- Decimal to percent
- Multiply by 100 (move the decimal two places right). 0.6 = 60%.
- Percent of a number
- Multiply the number by the percent as a decimal. 20% of 80 = 0.20 × 80 = 16.
- Finding the whole from a percent
- Divide the part by the percent as a decimal. If 15 is 25% of a number, the number is 15 ÷ 0.25 = 60.
- Percent change
- Change ÷ original × 100. Always divide by the starting value. From 80 to 100: 20 ÷ 80 = 25% increase.
- Percent increase shortcut
- To increase a number by 25%, multiply by 1.25; to decrease by 25%, multiply by 0.75.
- Ratio
- A comparison of two quantities, written 3:5, 3 to 5, or 3/5. Reduce ratios like fractions.
- Proportion
- An equation stating two ratios are equal, such as 2/3 = x/12. Solve by cross-multiplying: 3x = 24, so x = 8.
- Cross-multiplication
- For a/b = c/d, multiply diagonally: a × d = b × c. Used to solve proportions.
- Unit rate
- A rate with a denominator of 1, such as miles per hour or cost per item. Find it by dividing. 12for4lbs=3 per lb.
- Scale factor
- The ratio used to enlarge or reduce; multiply each measurement by it. A 1:50 map scale means 1 unit on the map equals 50 real units.
- Exponent
- A small number telling how many times to multiply the base by itself. 2³ = 2 × 2 × 2 = 8.
- Zero exponent rule
- Any nonzero number raised to the 0 power equals 1. 7⁰ = 1.
- Negative exponent
- A negative exponent means take the reciprocal: x⁻ⁿ = 1/xⁿ. So 2⁻³ = 1/8.
- Product of powers rule
- When multiplying like bases, add the exponents: xᵐ · xⁿ = xᵐ⁺ⁿ. So 2³ · 2⁴ = 2⁷.
- Quotient of powers rule
- When dividing like bases, subtract the exponents: xᵐ ÷ xⁿ = xᵐ⁻ⁿ. So 2⁵ ÷ 2² = 2³.
- Power of a power rule
- Raise a power to a power by multiplying the exponents: (xᵐ)ⁿ = xᵐⁿ. So (2³)² = 2⁶.
- Square root
- A value that, multiplied by itself, gives the number. √36 = 6 because 6 × 6 = 36.
- Perfect square
- The product of an integer with itself: 1, 4, 9, 16, 25, 36, 49, 64, 81, 100... Their square roots are whole numbers.
- Scientific notation
- A number written as a value between 1 and 10 times a power of 10. 47,000 = 4.7 × 10⁴.
- Estimating with rounding
- Replace numbers with nearby easy values to check that an answer is reasonable. 19 × 21 ≈ 20 × 20 = 400.
- Rounding to a place value
- Look at the digit to the right: 5 or more rounds up, 4 or less rounds down. 3.47 to the tenths = 3.5.
- Divisibility by 3
- A number is divisible by 3 if the sum of its digits is divisible by 3. 132 → 1+3+2 = 6, divisible by 3.
- Divisibility by 9
- A number is divisible by 9 if the sum of its digits is divisible by 9. 729 → 7+2+9 = 18, divisible by 9.
- Divisibility by 4
- A number is divisible by 4 if its last two digits form a number divisible by 4. 1,316 → 16 is divisible by 4.
- Even and odd numbers
- Even numbers are divisible by 2 (end in 0, 2, 4, 6, 8); odd numbers are not. Even × any = even; odd × odd = odd.
- Adding integers with different signs
- Subtract the absolute values and keep the sign of the larger one. −8 + 5 = −3.
- Multiplying signed numbers
- Same signs give a positive product; different signs give a negative product. (−4)(−3) = 12; (−4)(3) = −12.
- Subtracting integers
- Add the opposite: a − b = a + (−b). 5 − (−3) = 5 + 3 = 8.
- Number line ordering
- Numbers increase from left to right. −5 is less than −2, which is less than 0, which is less than 3.
- Comparing fractions
- Use a common denominator or cross-multiply. For 3/4 vs 5/7: 3×7 = 21 vs 5×4 = 20, so 3/4 is larger.
- Equivalent fractions
- Fractions that name the same value, found by multiplying or dividing top and bottom by the same number. 1/2 = 2/4 = 3/6.
- Reducing a fraction part of a recipe
- To make 2/3 of a recipe needing 3/4 cup, multiply: 2/3 × 3/4 = 6/12 = 1/2 cup.
- Place value
- The value of a digit based on its position. In 3,482 the 4 means 400 (hundreds place).
- Rounding money
- Round to the nearest cent (hundredths) by looking at the thousandths digit. 4.567≈4.57.
- Whole number
- The counting numbers plus zero: 0, 1, 2, 3, 4, ... No negatives, fractions, or decimals.
- Twin primes
- A pair of prime numbers that differ by 2, such as 11 and 13 or 17 and 19.
- Factors of a prime number
- Exactly two: 1 and the number itself. That is the definition of prime.
- Estimating a square root
- Find the perfect squares it falls between. √50 is between √49 = 7 and √64 = 8, so about 7.1.
- Converting units (length)
- Multiply or divide by the conversion factor. 3 feet = 36 inches (×12); 250 cm = 2.5 m (÷100).
- Converting units (time)
- 60 seconds = 1 minute, 60 minutes = 1 hour. 150 minutes = 2 hours 30 minutes.
- Dimensional analysis
- Multiply by conversion fractions so unwanted units cancel, leaving the desired unit. Lets you convert miles/hour to feet/second, etc.
- Percent greater than 100
- A percent over 100% means more than the whole. 150% of 40 = 1.5 × 40 = 60.
- Markup and discount
- Markup adds a percent to a price; discount subtracts one. A 50itemat2040.
- Simple interest
- I = Prt, where P is principal, r is the annual rate (as a decimal), and t is time in years. 1,000at5100.
- GCF supply-kit problem
- To split items into identical groups using all of them, find the GCF of the counts. 54 pencils and 72 erasers → GCF 18 kits.
- LCM 'line up again' problem
- To find when two repeating events coincide, find the LCM of their periods. Laps of 6 and 9 minutes meet again at 18 minutes.
- Fraction of a fraction
- 'Of' means multiply. 1/2 of 1/3 = 1/2 × 1/3 = 1/6.
- Sum of consecutive even multiples
- The sum 2a + 4a + ... + 2na is n(n+1)a, since 2a(1 + 2 + ... + n) = 2a · n(n+1)/2.
- Repeating decimal
- A decimal with a digit or block that repeats forever, written with a bar. 1/3 = 0.333... = 0.3̄.
- Terminating decimal
- A decimal that ends. A fraction terminates when its denominator (in lowest terms) has only 2s and 5s as factors. 3/8 = 0.375.
- Opposite (additive inverse)
- The number that adds to a given number to make 0. The opposite of 7 is −7.
- Cube of a number
- Multiply the number by itself three times. 4³ = 4 × 4 × 4 = 64.
- Square of a number
- Multiply the number by itself. 9² = 9 × 9 = 81.
- Properties: commutative
- Order does not change a sum or product. a + b = b + a; a × b = b × a.
- Properties: associative
- Grouping does not change a sum or product. (a + b) + c = a + (b + c).
- Properties: distributive
- a(b + c) = ab + ac. So 3(x + 4) = 3x + 12.
- Counting principle
- If one choice has m options and another has n options, the number of combined outcomes is m × n. 3 shirts × 4 pants = 12 outfits.
- Estimating a percent of a number
- Use friendly benchmarks. 10% of a number moves the decimal one place left; 50% is half; 25% is a quarter.
- Rate problem (distance)
- Distance = rate × time, so rate = distance ÷ time. 150 miles in 3 hours = 50 mph.
- Work / per-unit rate
- Divide total by quantity to get a per-unit value. 240 copies in 8 minutes = 30 copies per minute.
- Reading mixed numbers on a ruler
- Each inch is divided into halves, quarters, eighths, sixteenths. A mark halfway between 2 and 3 is 2½ inches.
- Estimating fractions near a benchmark
- Compare to 0, ½, or 1. 7/15 is just under ½; 9/10 is near 1.
- Order of magnitude
- The power of ten closest to a number. 6,200 is on the order of 10³ (thousands).
- Negative number subtraction trap
- Subtracting a negative is the same as adding. 3 − (−5) = 3 + 5 = 8 — a common careless error.
- Percent of change vs percentage points
- Going from 20% to 25% is a rise of 5 percentage points, but a 25% relative increase (5 ÷ 20). Keep them distinct.
- Comparing rational and irrational
- Rational numbers terminate or repeat; irrationals (π, √2) do neither. π ≈ 3.14159... never repeats.
- Estimating to check a calculation
- Round each value first to confirm an exact answer is reasonable. If 4.9 × 9.8 ≈ 5 × 10 = 50, then 48.02 is sensible.
- Splitting a quantity by a ratio
- Add the ratio parts, divide the total by that sum, then multiply. Share 60ina1:2:3ratio→partsof10, 20,30.
- Fraction word problem keywords
- 'Of' means multiply, 'per' means divide, 'is' means equals. Translate the words into an operation.
- Like fractions vs unlike fractions
- Like fractions share the same denominator and can be added directly; unlike fractions need a common denominator first.
- Estimating products and quotients
- Round each factor to a friendly number to predict the size of the answer before computing exactly.
- Comparing decimals
- Line up the decimal points and compare digit by digit from the left. 0.4 > 0.38 because 0.40 > 0.38.
- Estimating a tip
- 10% is the decimal moved one place; 20% is double that. A 20% tip on 30isabout6.
- Average rate over a whole trip
- Total distance ÷ total time, not the average of the speeds. Compute each leg's distance and time first.
- Mean (average)
- Add all the values and divide by how many there are. The mean of 6, 8, 8, 10, 13 is 45 ÷ 5 = 9.
- Median
- The middle value of an ordered data set. With an even count, average the two middle numbers. Median of 12, 15, 19, 22, 27, 31 is (19+22)/2 = 20.5.
- Mode
- The value that appears most often. In 14, 16, 16, 15, 16, 14, 17 the mode is 16. A set can have no mode or several.
- Range
- The largest value minus the smallest. For 8, 3, 7, 14, 10, 6, 2, 9 the range is 14 − 2 = 12.
- Mean vs median with outliers
- The mean is pulled toward extreme values; the median resists them. For skewed data (incomes, home prices) the median better represents the center.
- Standard deviation
- A measure of how spread out data is around the mean. A larger standard deviation means more spread; a value of 0 means all data points are identical.
- Effect of removing a value on the mean
- Removing a number above the mean lowers the average; removing one below it raises the average. Recompute with the new sum and count.
- Weighted average
- Multiply each value by its weight (or count), add, then divide by the total weight. A grade with a heavier final counts that score more.
- Probability of an event
- Favorable outcomes ÷ total equally likely outcomes, a value from 0 to 1. Rolling a 4 on a die has probability 1/6.
- Probability of independent events (AND)
- Multiply the probabilities. P(A and B) = P(A) × P(B). Two events with 0.6 and 0.8 → 0.48.
- Probability of either event (OR)
- Add and subtract the overlap. P(A or B) = P(A) + P(B) − P(A and B).
- Complement of an event
- The chance the event does NOT happen: P(not A) = 1 − P(A). If P(rain) = 0.3, P(no rain) = 0.7.
- Independent events
- Events where one outcome does not affect the other, like separate coin flips. Their probabilities multiply.
- Dependent events
- Events where the first outcome changes the second's probability, like drawing cards without replacing them.
- Theoretical vs experimental probability
- Theoretical comes from equally likely outcomes; experimental comes from actual trial results. Over many trials, experimental approaches theoretical.
- Bar graph
- Uses rectangular bars to compare amounts across categories. Bar length shows the value; read the axis scale carefully.
- Line graph
- Shows how a quantity changes over time using points connected by line segments. Good for trends.
- Circle (pie) graph
- Shows parts of a whole as sectors; the whole circle is 100%. A 25% slice is a quarter of the circle (90°).
- Histogram
- A bar graph for grouped numerical data; bars touch and each covers an interval (bin). Shows the shape of a distribution.
- Scatterplot
- Plots paired data as points to show the relationship between two variables. A rising pattern suggests a positive correlation.
- Positive correlation
- As one variable increases, the other tends to increase. On a scatterplot the points trend upward to the right.
- Negative correlation
- As one variable increases, the other tends to decrease. On a scatterplot the points trend downward to the right.
- Correlation is not causation
- Two variables moving together does not prove one causes the other; a third factor may explain both.
- Line of best fit (trend line)
- A straight line through scatterplot points that summarizes the trend, used to estimate and predict values.
- Two-way (frequency) table
- Organizes data by two categories in rows and columns. Read the correct row and column to find a count or a conditional rate.
- Skewed data
- Data with a long tail to one side. Right-skewed: mean > median; left-skewed: mean < median. The tail points toward the mean.
- Positively (right) skewed
- A distribution with a long right tail caused by a few large values. The mean is greater than the median.
- Negatively (left) skewed
- A distribution with a long left tail caused by a few small values. The mean is less than the median.
- Symmetric distribution
- A distribution where the two halves mirror each other; the mean and median are approximately equal.
- Outlier
- A value far from the rest of the data. Outliers strongly affect the mean and the range but barely move the median.
- Quartiles
- Three values (Q1, Q2/median, Q3) that split ordered data into four equal parts. Q1 is the 25th percentile, Q3 the 75th.
- Interquartile range (IQR)
- Q3 − Q1, the spread of the middle 50% of the data. It resists outliers.
- Box plot (box-and-whisker)
- Displays the five-number summary: minimum, Q1, median, Q3, and maximum. The box spans the IQR.
- Percentile
- The percent of data values at or below a given value. Scoring in the 80th percentile means you did as well as or better than 80% of test takers.
- Sample vs population
- A population is the entire group; a sample is the subset actually studied. A good sample is random and representative.
- Random sample
- A sample in which every member of the population has an equal chance of being chosen, reducing bias.
- Biased sample
- A sample that is not representative of the population, giving misleading results. A survey only of volunteers is biased.
- Frequency
- The number of times a value or category occurs in a data set. A frequency table lists each value with its count.
- Relative frequency
- A category's count divided by the total, often written as a fraction, decimal, or percent. It estimates probability.
- Measures of center
- Mean, median, and mode — each describes a 'typical' value differently. The best one depends on the shape of the data.
- Measures of spread
- Range, interquartile range, and standard deviation — they describe how spread out the data is.
- Reading a graph's scale
- Check the axis intervals before estimating values; gridlines may count by 2s, 5s, 10s, etc.
- Misleading graph
- A graph can distort data with a truncated axis, unequal intervals, or 3-D effects. Always read the actual numbers.
- Expected value (long-run average)
- Multiply each outcome by its probability and add. The long-run average result of a repeated random process.
- Probability with 'and replacement'
- Replacing the item keeps each draw independent, so probabilities stay the same and multiply.
- Probability without replacement
- Not replacing the item changes the totals, making draws dependent; recompute the probability for each later draw.
- Combination vs permutation
- A permutation counts ordered arrangements; a combination counts groups where order does not matter. 'Choosing 3' usually means a combination.
- Probability of mutually exclusive events
- Events that cannot happen together; their joint probability is 0, so P(A or B) = P(A) + P(B).
- Interpreting a survey percentage
- Apply the percent to the relevant total. If 30% of 250 students walk to school, that is 0.30 × 250 = 75 students.
- Comparing two data sets
- Compare both center (mean/median) and spread (range/standard deviation). Equal means can hide very different spreads.
- Cumulative frequency
- A running total of frequencies; each entry adds the previous counts. Used to find medians and percentiles.
- Stem-and-leaf plot
- Splits each value into a stem (leading digits) and a leaf (last digit) to show the distribution while keeping the data.
- Probability scale
- Probabilities range from 0 (impossible) to 1 (certain). 0.5 means equally likely to happen or not.
- Sample space
- The set of all possible outcomes of an experiment. For one die roll the sample space is {1, 2, 3, 4, 5, 6}.
- Odds vs probability
- Probability compares favorable outcomes to the total; odds compare favorable to unfavorable. Probability 1/4 is odds of 1 to 3.
- Estimating from a circle graph
- Multiply the slice's percent by the total. A 40% slice of a 2,000budgetis0.40×2,000=800.
- Trend in a line graph
- A rising line shows increase, a falling line shows decrease, and a flat line shows no change over the interval.
- Mean of a frequency table
- Multiply each value by its frequency, add those products, and divide by the total frequency.
- Bimodal data set
- A data set with two values that tie for most frequent; it has two modes. The distribution shows two peaks.
- Predicting from a line of best fit
- Read the trend line at the desired x-value to estimate y. Extrapolating far beyond the data is unreliable.
- Variable
- A letter that represents an unknown or changing number, such as x or n in an expression or equation.
- Algebraic expression
- A combination of numbers, variables, and operations with no equals sign, such as 3x + 5.
- Equation
- A statement that two expressions are equal, containing an equals sign, such as 2x + 3 = 11.
- Like terms
- Terms with the same variable raised to the same power; only like terms can be combined. 3x and 5x combine to 8x.
- Solving a one-step equation
- Undo the operation on both sides. For x + 7 = 12, subtract 7: x = 5.
- Solving a two-step equation
- Undo addition/subtraction first, then multiplication/division. For 4x − 7 = 21: add 7 (4x = 28), divide by 4 (x = 7).
- Solving equations with variables on both sides
- Collect variables on one side and numbers on the other. 3(x + 2) = 5x − 4 → 3x + 6 = 5x − 4 → x = 5.
- Inequality symbols
- < less than, > greater than, ≤ less than or equal to, ≥ greater than or equal to.
- Solving an inequality
- Solve like an equation, with one rule: flip the inequality sign when you multiply or divide both sides by a negative number.
- Inequality sign-flip rule
- Multiplying or dividing by a negative reverses the inequality. −3x > 12 → x < −4 (sign flips).
- Slope
- The steepness of a line: rise over run, the change in y divided by the change in x. In y = mx + b, the slope is m.
- Slope formula
- For points (x₁, y₁) and (x₂, y₂): slope = (y₂ − y₁) ÷ (x₂ − x₁). Through (2, 3) and (6, 11): (11−3)/(6−2) = 2.
- Slope-intercept form
- y = mx + b, where m is the slope and b is the y-intercept (where the line crosses the y-axis).
- Y-intercept
- The point where a line crosses the y-axis, where x = 0. In y = 2x + 5 the y-intercept is 5.
- X-intercept
- The point where a line crosses the x-axis, where y = 0. Set y = 0 and solve for x.
- Slopes of horizontal and vertical lines
- A horizontal line has slope 0; a vertical line has an undefined slope.
- Parallel lines
- Lines that never meet; they have equal slopes but different y-intercepts.
- Perpendicular lines
- Lines that meet at a right angle; their slopes are negative reciprocals (their product is −1).
- System of equations
- Two or more equations solved together; the solution is the point satisfying all of them — where the graphs intersect.
- Substitution method
- Solve one equation for a variable, substitute it into the other, and solve. Good when a variable is already isolated.
- Elimination method
- Add or subtract the equations to cancel one variable, then solve. Multiply an equation first if needed to match coefficients.
- Evaluating an expression
- Substitute the given value for the variable and simplify. For 3x + 4 when x = 5: 3(5) + 4 = 19.
- Translating words to algebra
- 'More than' is +, 'less than' is −, 'product' is ×, 'quotient' is ÷. 'Five less than twice a number' is 2x − 5.
- Function
- A rule that assigns exactly one output to each input. Written f(x); f(3) means evaluate the rule at x = 3.
- Distributing then solving
- Use the distributive property to clear parentheses before combining like terms. 2(x + 3) = 10 → 2x + 6 = 10 → x = 2.
- Perimeter
- The distance around a figure — the sum of all side lengths. A rectangle's perimeter is 2(length + width).
- Area of a rectangle
- length × width. A 9 cm by 4 cm rectangle has an area of 36 square centimeters.
- Area of a triangle
- ½ × base × height. A triangle with base 10 and height 6 has area ½ × 10 × 6 = 30 square inches.
- Area of a circle
- π × radius². With radius 5 and π ≈ 3.14, area ≈ 3.14 × 25 ≈ 79 square units.
- Circumference of a circle
- π × diameter (or 2 × π × radius). A circle with diameter 8 and π ≈ 3.14 has circumference ≈ 25 units.
- Area of a parallelogram
- base × height, where height is the perpendicular distance between the parallel sides.
- Area of a trapezoid
- ½ × (base₁ + base₂) × height — the average of the parallel sides times the height between them.
- Volume of a rectangular prism (box)
- length × width × height. A 5 × 3 × 4 box has a volume of 60 cubic units.
- Volume of a cylinder
- π × radius² × height. A cylinder with radius 3 and height 4 has volume π × 9 × 4 = 36π cubic units.
- Surface area
- The total area of all faces of a 3-D figure, measured in square units. Add the areas of each face.
- Pythagorean theorem
- For a right triangle with legs a and b and hypotenuse c: a² + b² = c². A 3-4-5 triangle satisfies it (9 + 16 = 25).
- Hypotenuse
- The longest side of a right triangle, opposite the right angle. The Pythagorean theorem finds it from the two legs.
- Types of triangles by sides
- Equilateral (3 equal sides), isosceles (2 equal sides), scalene (no equal sides).
- Types of triangles by angles
- Acute (all angles < 90°), right (one 90° angle), obtuse (one angle > 90°).
- Sum of a triangle's interior angles
- Always 180°. If two angles are 50° and 60°, the third is 180° − 110° = 70°.