# 7.2 Identities: Cofunction, Double-Angle, and Half-Angle

Use cofunction identities to derive other identities.

Use the double-angle identities to find function values of twice an angle when one function value is known for that angle.

Use the half-angle identities to find function values of half an angle when one function value is known for that angle.

Simplify trigonometric expressions using the double-angle identities and the half-angle identities.

# Cofunction Identities

Each of the identities listed below yields a conversion to a *cofunction*. For this reason, we call them cofunction identities.

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