if 9^y=x, which of the following represents 9^y-9^(y-3)

Question

A) 1/x^3
B) x^3
C) 729x
D) 729/728 x
E) 728/729 x

Answer 1

9^y = x, so

9^y-9^(y-3) = 9^y - 9^y/9^3 = x - x/729 = ...