PLEASE HELP

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

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 length of the midsegment of a trapezoid with bases of length 15 and 25 ?