I need help on these problems they are from my study guide and i don't have a clue on how to do these 3 problems and if anyone can show the steps and somewhat explain the steps so i can do it myself next time. 1.)

could someone please refresh my memory of the basic trig functions? ex) cos^2 + sin^2 = 1? That is a trig identity. http://www.sosmath.com/trig/Trig5/trig5/trig5.html

Suppose that z1=6-8i. Find: A. The Trig Form of the complex number z1, where your theta is in degrees. B. The Trig form of z1*z2, where z2=5[cos(60degrees)+isin(60degrees)] C. The Trig Form of (z1)^4