(3a²+2a-8)²-(a²-2a-8)²=(3a²+2a-8+a²-2a-8)(3a²+2a-8-a²+2a+8)=(4a²-16)(2a²+4a)=4×2×a(a²-4)(a+2)=8a(a+2)(a-2)(a+2)=8a(a+2)²(a-2)