Question

How do you use the product to sum formulas to write `sin(theta+pi)sin(theta-pi)` as a sum or difference?

Answer 1

• cos t

Explanation:

Use trig identity:
`sin a.sin b = cos ((a - b)/2) - cos ((a + b)/2)`
In this case:

`sin (t + pi)(sin (t - pi) = cos pi - cos t = 0 - cos t = - cos t`