2x^4+7x^3-2x^2-13x+6
=2x^4+7x^3+3x^2-5x^2-13x+6
=x^2(2x+1)(x+3)-(5x-2)(x+3)
=(x+3)[x^2(2x+1)-(5x-2)]
=(x+3)(2x^3+x^2-2x-3x+2)
=(x+3)[(2x^3-2x)+(x^2-3x+2)]
=(x+3)[2x(x^2-1)+(x-2)(x-1)]
=(x+3)[2x(x+1)(x-1)+(x-2)(x-1)]
=(x+3)(x-1)[2x(x+1)+x-2]
=(x+3)(x-1)(2x^2+3x-2)
=(x+3)(x-1)(2x-1)(x+2)