14. DOUBLE-ANGLE IDENTITIES

If we want to know a formula for we could use the sum formula. we can trade these places

Let's try the same thing for This is the double angle formula for cosine but by substiuting some identities we can express it in a couple other ways.

Double-angle Formula for Tangent

Summary of Double-Angle Formulas

Double-Angle Identities Simplify

Double-Angle Identities Simplify

Double-Angle Identities Simplify

Double-Angle Identities Simplify

Double-Angle Identities Verify the identity

Double-Angle Identities Verify the identity

Identities Prove

Let's draw a picture. 5 4   -3

Let's draw a picture.  1  4