What is the answer to this question

Determine whether the set of whole numbers is closed under addition. explain why the set is or is not closed. give an example.

Which sum or difference identity would you use to verify that cos (180° - q) = -cos q? a.) sin (a -b) = sin a cos b – cos a sin b b.) cos (a -b) = cos a cos b – sin a sin b c.) cos (a -b) = cos a cosb + sin a sin b d.) sin (a + b) = sin a cos b + cos a sin b

What is the measure of angle x? a.101 b.158 c.44 d.79