15. Simplify sin (90° - O) cos 0 - sin (180° + 0) sin e.

Answer: cos² (θ) + sin (θ) sin (e)

Step-by-step explanation:

sin (90° - θ) cos (Ф) - sin (180° + θ) sin (e)

Note the following identities:

sin (90° - θ) = cos (x)

sin (180° + θ) = - sin (x)

Substitute those identities into the expression:

cos (x) cos (x) - - sin (x) sin (e)

= cos² (x) + sin (x) sin (e)