(x+2y)²×(x-2y)²-(x+4y)²应该是(x+2y)²×(x-2y)²-(x²+4y²)²

问题描述:

(x+2y)²×(x-2y)²-(x+4y)²
应该是(x+2y)²×(x-2y)²-(x²+4y²)²

(x+2y)²×(x-2y)²-(x²+4y²)²
=[(x+2y)×(x-2y)]²-(x²+4y²)²
=(x²-4y²)²-(x²+4y²)²
=[(x²-4y²)+(x²+4y²)]×[(x²-4y²)-(x²+4y²)]
=2x²×(-8y²)
=-16x²y²

(x+2y)²×(x-2y)²-(x+4y)²=(x²-4y²)²-(x²+4y)²=2x²*(-8y²)=-16x²y²
知道,我就是按你改后的题解得,一看就能看到你哪里写错了.