Test Prep (ACT/SAT/PERT) Vocab

Written By Tara Griffin

Numbers & Types

  • Integer: Whole numbers (positive, negative, or zero); no fractions or decimals
    Ex: -3, 0, 7

  • Rational number: Can be written as a fraction (includes integers, terminating or repeating decimals)

  • Irrational number: Cannot be written as a fraction; decimal goes on without repeating
    Ex: √2, π

  • Real number: All rational and irrational numbers

  • Imaginary number: Involves i, where √-1 = i

  • Prime number: Has exactly two positive factors: 1 and itself
    (First few: 2, 3, 5, 7, 11, 13...)

  • Even/Odd:

    • Even: divisible by 2

    • Odd: not divisible by 2

Algebra Terms

  • Variable: A symbol (like x or y) representing a number

  • Coefficient: A number multiplied by a variable
    (In 5x, 5 is the coefficient)

  • Constant: A fixed number with no variable attached

  • Expression: A math phrase with no equal sign
    (Ex: 3x+2)

  • Equation: Two expressions equal to each other
    (Ex: 3x+2=11)

  • Inequality: A comparison using <, >, ≤, or ≥

  • Solution/Root: A value that makes an equation true

  • System of equations: Two or more equations solved together

Geometry Terms

  • Angle: Formed by two rays meeting at a point

  • Right angle: 90°

  • Acute angle: < 90°

  • Obtuse angle: > 90° but < 180°

  • Complementary angles: Add to 90°

  • Supplementary angles: Add to 180°

  • Congruent: Equal in shape and size

  • Similar: Same shape, proportional sides, equal angles

  • Perpendicular: Lines that meet at 90°

  • Parallel: Lines that never meet, same slope

  • Radius: Distance from center of a circle to edge

  • Diameter: Distance across a circle through the center (2 × radius)

  • Circumference: Distance around a circle (C=2πr)

Statistics Terms

  • Mean: Average

  • Median: Middle value when sorted

  • Mode: Most frequent value

  • Range: Highest − lowest

  • Standard deviation: Measure of data spread

  • Probability: Likelihood = favorable outcomes / total outcomes

Other Common Terms

  • Factor: A number that divides evenly into another

  • Multiple: A number you get by multiplying

  • Greatest common factor (GCF): Largest number dividing evenly into two or more numbers

  • Least common multiple (LCM): Smallest number that is a multiple of two or more numbers

  • Function: Each input (x) has one output (f(x)); passes the vertical line test

  • Domain: All valid inputs (x-values)

  • Range: All resulting outputs (y-values)

  • Slope: Rate of change = rise/run

  • Intercept: Where a graph crosses an axis

    • x-intercept: y = 0

    • y-intercept: x = 0

Tara Griffin
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Fraction Basics: A Parent's Guide to Practical Math