Dialiate (-2,3) by scale factor of 2

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

Hi, can anyone show me how to do this problem? 100 points for this. in advance

Which property was used to simplify the expression? 3c+9 +4c=3c+4c+9