= 4x^3+2x^2+6x^2- 15x-9

= 2x^2(2x+ 1)+3(2x^2-5x-3)

= 2x^2(2x+ 1)+3(x-3)(2x+ 1)

= (2x^2+3x-9)(2x+ 1)

= (2x-3)(x+3)(2x+ 1)

(2) I'm still thinking about the solution to the first question, which is almost to add an x 2 minus an x 2 times the back fork, and then factorize the front fork.

I haven't found the right number after calculating for a long time.