a2-b2=(a-b)(a+b)
(8-x)*(8+x)=-2
(a-8)*(a+8)=2-
(8-cd)*(8+cd)=-()2
(7b-8)*(7b+8)=*2-
(7b-8)*(7b+8)=(*)2-
(15-m)*(15+m)=-2
(z-15)*(z+15)=2-
(15-cd)*(cd+15)=-()2
(8b-15)*(8b+15)=*2-
(8b-15)*(15+8b)=(*)2-
(7ab-zx)*(zx+7ab)=*()2-()2
(7z+a)*(a-7z)=2-*2
(mlu+7k)*(7k-mlu)=*2-()2
(15bc3-7x)*(7x+15bc3)=*b2c6-*2
(15bc3-7x)*(7x+15bc3)=(*bc3)2-*2