Use a​ sum-to-product identity to rewrite the expression.

Question

^cos (8t²) - cos (5t²)

a. -2 sin (6.5t²) sin (1.5t²)

b. -2 cos (6.5t²) cos (1.5t²)

c. -2 sin (6.5t²) cos (1.5t²)

d. -2 cos (6.5t²) sin (1.5t²)

Answer 1

I substituted 15 for "t". a) is your answer. (.2928932188)

Answer 2

cos u - cos v = -2sin ((u + v)/2)sin((u - v)/2)

cos 8t² - cos 5t² = -2(6.5t²)sin(1.5t²)