Evaluate cos (11π/12) as cos (π/4 + 2π/3).

Using the Addition Formulas

Use the addition formulas to derive the identities in Exercises 31–36.

sin (x − π/2) = −cos x

Using the Addition Formulas

Use the addition formulas to derive the identities in Exercises 31–36.

sin (A − B) = sin A cos B − cos A sin B

In Exercises 39–42, express the given quantity in terms of sin x and cos x.

cos (3π/2 + x)

What happens if you take B = 2π in the addition formulas? Do the results agree with something you already know?

Evaluate sin (5π/12).

Using the Half-Angle Formulas

Find the function values in Exercises 47–50.

cos² 5π/12

Using the Half-Angle Formulas

Find the function values in Exercises 47–50.

sin² 3π/8

Solving Trigonometric Equations

For Exercises 51–54, solve for the angle θ, where 0 ≤ θ ≤ 2π.

sin² θ = cos² θ