How to find missing angles in parallelograms

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

What is the perimeter of square abcd? units units 28 units 37 units

Find the area of a parallelogram with base 15 yards and height 21 2/3