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