ACT - Math Vocabulary & Formulas

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quadratic formula

[-b ± √(b² - 4ac)] / (2a)

slope formula

(y₂- y₁) / (x₂- x₁)


..., -3, -2, -1, 0, 1, 2, 3, ...


fractions (anything expessable as a ratio of integers)


integers, rationals, plus special #s (like √2 or pi)

order of opperations

PEMDAS (Parentheses / Exponents / Multiply / Divide / Add / Subtract)

Arithmetic Sequences

t₁, t₁+ d, t₁+2d, ...

Geometric Sequences

t₁, t₁· r, t₁· r², ...


ex. factors of 52 are 2, 4, 13, and 26


ex. multiples of 20 are 40, 60, 80, 100, ...


part = (percent / 100) x whole


average = sum of terms / number of terms

average speed

average speed = total distance / total time


sum = average x (number of terms)


mode = value in the list that appears most often


median = middle value in the list

fundamental counting principle

if an event can happen in N ways, and another, independent event can happen in M ways, then both events together can happen in N x M ways.


probability = number of desired outcomes / number of total outcomes

adding exponents

x^a · x^b = x^(a+b)

subtracting exponents

x^a / x^b = x^(a-b)

negative exponents

1 / x^b = x^(-b)

multiplying exponents

(x^a)^b = x^(a·b)


√(xy) = √x · √y


(x+a)(x+b) = x^2 + (b+a)x + ab

difference of squares

a^2 -b^2 = (a+b)(a-b)

a^2 + 2ab + b^2


a^2 - 2ab + b^2


distance formula

√[(x₂- x₁)^2 + (y₂- y₁)^2)]

mid-point formula

[(x₁+ x₂)/2 , (y₁+ y₂)/2]

intersecting lines

opposite angles are equal (each pair of angles along the same line add to 180 degrees)

area of triangle

area = (1/2)bh

angles of triangle

add up to 180 degrees

length of triangle sides

length of 1 side is always less than the sum of the other 2


three equal sides, all angles = 60 degrees


2 equal sides, 2 equal angles


same shape, corresponding angles are equal, corresponding sides are in proportion

circle area

pi · r^2

circle circumference

2 · pi · r

full circle

= 360 degrees

length of arc

(n degree / 360 degrees) · 2 · pi · r

area of sector

(n degree / 360 degrees) · pi · r^2

rectangle area

area = lw

parallelogram area

area = lh

rectangular solid volume

volume = lwh

right cylinder volume

volume = pi · r^2 · h

prime factors

2, 3, 5, 7, 11, ...

Greatest Common Factor

ex. GCF of 200 and 60 is 20

Least Common Multiple

ex. LCM of 200 and 60 is 600

equation of circle

with midpoint (h,k) ... (x - h)^2 + (y - k)^2 = r^2


y = log(little b)x asks b^y = x

complex numbers

i^0 = 1; i^1 = i; i^2 = -1; i^3 = -i; i^4 = 1; i^5 = i; i^6 = -1; i^7 = -i

sin of an angle

opp / hyp

cos of an angle

adj / hyp

tan of an angle

opp / adj

special sin cos relationship

sin^2(angle) + cos^2(angle) = 1

degree to radian

degree# · (pi / 180 degrees)

radian to degree

radian# · (180 degrees / pi)

trapezoid area

area = [(base1 + base2) / 2] · h

Direct Variation


Inverse Variation


Slope intercept form


Point-Slope form

y - y₁= m(x - x₁)

standard form

Ax + By=C, where A, B, and C are not decimals or fractions, where A and B are not both zero, and where A is not a negative

Dividing by a negative number in an inequality

You must flip the sign

Graphing < or > on a coordinate plane

dotted line

Graphing ≥ or ≤ on a coordinate plane

solid line

Graphing ≥ or > on a coordinate plane

shade upwards or to the right

Graphing ≤ or < on a coordinate plane

shade downwards or to the left

circle perimeter

2 pi r


The distance from one point on the circle to another point on the circle.


The part of a circle that looks like a piece of pie. A sector is bounded by 2 radii and an arc of the circle.


Part of a circle connecting two points on the circle.

Central Angle

An angle whose vertex is the center of the circle

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