Factor 15a^5-5a^2
Start with 5a^2*(3a^3 -1)
The term in parentheses can be written as b^3 -1, where b = (3^1/3)*a, and factored into two terms, (b-1)(b^2 +2b + 1)
The term in parentheses can be written as b^3 -1, where b = (3^1/3)*a, and factored into two terms, (b-1)(b^2 +2b + 1)