(2x^2+6x+1)(x^2+3x-2)-18
=[2(x²+3x)+1](x²+3x-2)-18
=2(x²+3x)²-3(x²+3x)-2-18
=2(x²+3x)²-3(x²+3x)-20
=[2(x²+3x)+5]*[(x²+3x)-4]
=(2x²+6x+5)*(x²+3x-4)
=(2x²+6x+5)*(x+4)(x-1)