Question

Factor 63a^5-21a^7

Answer 1

\[-21 a^5 \left(a^2-3\right) \]

Answer 2

look at the factors or each term:
63a^5 = 3*3*7*a*a*a*a*a
21a^7 = 3*7 * a*a*a*a*a*a*a

take out anything that is COMMON to both terms and that will be your greatest common factor....