AP Precalculus: Trigonometric Identities

Flashcards highlighting key trigonometric identities and formulas from precalculus.

csc x

Reciprocal of sin x; csc x = 1/sin x

sec x

Reciprocal of cos x; sec x = 1/cos x

cot x

Reciprocal of tan x; cot x = 1/tan x

tan x

Defined as tan x = sin x / cos x

cot x

Defined as cot x = cos x / sin x

Pythagorean Identity

sin² x + cos² x = 1

tan² x + 1

Equals sec² x

1 + cot² x

Equals csc² x

sin(A + B)

Equals sin A cos B + cos A sin B

cos(A + B)

Equals cos A cos B - sin A sin B

sin(2x)

Double-Angle identity; sin(2x) = 2 sin x cos x

cos(2x) (First Form)

Equals cos² x - sin² x

cos(2x) (Second Form)

Equals 1 - 2sin² x

cos(2x) (Third Form)

Equals 2cos² x - 1