The diamter of a sphere is a line segamnet

Find the value of a. the diagram is not to scale. a quadrilateral is drawn. the upper and lower sides are parallel. the interior angle in the upper left corner is labeled a degrees. the angle in the upper right corner is labeled 113 degrees. the angle in the lower right corner is labeled b degrees. the angle in the lower left corner is labeled 36 degrees. a. 36 b. 144 c. 54 d. 126

Find the value of the cosine for angle a

What are the coordinates of the midpoint of ab? ,1/2) /2,-1) ,-3/2) /2,-2)