High School · Trigonometric Functions

CCSS.MATH.CONTENT.HSF.TF.C.9

(+) Prove the addition and subtraction formulas for sine, cosine, and tangent and use them to solve problems.

Read this standard on the official Common Core site

Lessons that teach this standard

• Double-Angle and Half-Angle Formulas

  Derive sin 2θ, cos 2θ and tan 2θ from the sum formulas, reverse them into half-angle and power-reducing forms, and use them for exact values and equations.

• Sum and Difference Formulas for Sine, Cosine and Tangent

  Why cos(α − β) = cos α cos β + sin α sin β, proved by rotating a chord of the unit circle, how the other formulas follow, and how to find exact values like cos 15°.