Question

Simplify the expression using the appropriate identities. (Do not use calculator)

sin 9° cos 10°- cos 9º sin 10° =

Answer 1

sin -1 degrees.

Explanation:

sin (A - B) = sin A cos B - cos A sin B

Therefore sin 9° cos 10°- cos 9º sin 10° = sin (9 - 10)

= sin -1 degrees.