Trigonometric Identities

Sine Cofunction Identity

sin(θ) = cos(90°−θ)

Cosine Cofunction Identity

cos(θ) = sin(90°−θ)

Tangent Cofunction Identity

tan(θ) = cot(90°−θ)

Cotangent Cofunction Identity

cot(θ) = tan(90°−θ)

Secant Cofunction Identity

sec(θ) = csc(90°−θ)

Cosecant Cofunction Identity

csc(θ) = sec(90°−θ)

Geometry (Reciprocal) Identities

Quotient Identities

Pythagorean Identities: Primary Pythagorean Identity

Pythagorean Identities: Tangent–secant identity

Pythagorean Identities: Cotangent–cosecant identity

Addition & Subtraction Identities: Sine Subtraction

Mnemonic device: Some Cows Can Sing

Addition & Subtraction Identities: Sine Addition

Mnemonic device: Some Cows Can Sing

Addition & Subtraction Identities: Cosine Subtraction

Mnemonic device: Chocolate Covered Sweet Strawberries

Addition & Subtraction Identities: Cosine Addition

Mnemonic device: Chocolate Covered Sweet Strawberries

Tangent of the Difference: Tangent Addition

Mnemonic device: Tim Takes Over One Tiny Town

Tangent of the Difference: Tangent Subtraction

Mnemonic device: Tim Takes Over One Tiny Town

Double Angle Identities: Sine

Double Angle Identities: Cosine

Double Angle Identities: Tangent