(3x²+2x-8)^2-(x²-2x-8)^2=(3x²+2x-8+x²-2x-8)(3x²+2x-8-x²+2x+8)=(4x²-16)(2x²+4x)=8(x²-4)(x²+2x)=8x(x+2)²(x-2)