2a^3+9a^2b+7ab^2-6b^3
=2a^3+6a^2b+3a^2b+9ab^2-2ab^2-6b^3
=2a^2*(a+3b)+3ab(a+3b)-2b^2(a+3b)
=(2a^2+3ab-2b^2)(a+3b)
=(2a-b)(a+2b)(a+3b)
2a^3+9a^2b+7ab^2-6b^3
=2a^3+6a^2b+3a^2b+9ab^2-2ab^2-6b^3
=2a^2*(a+3b)+3ab(a+3b)-2b^2(a+3b)
=(2a^2+3ab-2b^2)(a+3b)
=(2a-b)(a+2b)(a+3b)