Use the identities for the cosine of a sum or difference to write each expression as a trigonometric function of θ alone.
cos(270° + θ)

Write each function as an expression involving functions of θ or x alone. See Example 2.

tan(180° + θ)

Use the identities for the cosine of a sum or difference to write each expression as a trigonometric function of θ alone.

cos(θ - 270°)

Write each function as an expression involving functions of θ or x alone. See Example 2.

sin(π + x)

Express each function as a trigonometric function of x. See Example 5.

cos 3x

Express each function as a trigonometric function of x. See Example 5.

cos 4x

Find cos(s + t) and cos(s - t).

cos s = - 8/17 and cos t = - 3/5, s and t in quadrant III

Find cos(s + t) and cos(s - t).

sin s = 2/3 and sin t = -1/3, s in quadrant II and t in quadrant IV

Find cos(s + t) and cos(s - t).

cos s = √2/4 and sin t = - √5/6, s and t in quadrant IV