Please help me with this question

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

If cos(2x) = tan^2(y), show that cos(2y) = tan^2(x).

If 30 lb of rice and 30 lb of potatoes cost ? $27.60? , and 20 lb of rice and 12 lb of potatoes cost ? $15.04? , how much will 10 lb of rice and 50 lb of potatoes? cost?