第一个题有问题;
第二个题运用平方差公式就可以了
1. =(x-y)^2*(5m^3)^2-(x-y)^2*(8n^2*(x-y))^2
=(x-y)^2*((5m^3)^2-(8n^2*(x-y))^2)
=(x-y)^2*(5m^3+8n^2*(x-y))*(5m^3-8n^2*(x-y))
2. =(7(a-b))^2-(a+b)^2
=(7a-7b-a-b)(7a-7b+a+b)
=(6a-8b)(8a-6b)
=4(3a-4b)(4a-3b)