ACT Math Formulas

Area of a triangle

Area of a circle

A = π r ²

Circumference of a circle

C = 2π r

Volume of a cylinder

V = π r ² h

Law of Sines

Must know side + opposite angle + something else: AAS, ASA, SSA

Law of Cosines

Use with 2 sides and angle between then or all three sides: SAS, SSS

Distance formula

Midpoint

Circle equation

Circle centered at ( h , k ) = ( x – h ) ² + ( y – k ) ² = r ²

Rational #

Able to be written as a fraction, top and bottom are both integers

Irrational #

Repeating decimal without pattern

Arithmetic sequence

Geometric sequence

Permutation (# of ways to arrange/order a group of things)

where n is the number of elements available and r is the number of elements chosen

where ORDER MATTERS

Combination (# of ways to make different groups out of a group of things)

where n is the number of elements available and r is the number of elements chosen

Where ORDER DOESN’T MATTER

45-45-90 special right triangle

30-60-90 special right triangle

Sum of angles in a n-sided polygon

( n – 2)180°

Circle formula

( x – h ) ² + ( y – k ) ² = r ²

Standard equation of ellipse

Width 2a, height 2b, center (h,k)