Need help 8th grade math

Proceed as in example 3 in section 6.1 to rewrite the given expression using a single power series whose general term involves xk. ∞ n(n − 1)cnxn − 2 n = 2 − 4 ∞ ncnxn n = 1 + ∞ cnxn n = 0

What is the circumference of the pie

Astraight water slide is 175 feet above ground and is 200 feet long. what is the angle of depression to the bottom of the slide?