a2-b2=(a-b)(a+b)
(2-x)*(2+x)=-2
(a-2)*(a+2)=2-
(2-cd)*(2+cd)=-()2
(7b-2)*(7b+2)=*2-
(7b-2)*(7b+2)=(*)2-
(3-m)*(3+m)=-2
(z-3)*(z+3)=2-
(3-cd)*(cd+3)=-()2
(2b-3)*(2b+3)=*2-
(2b-3)*(3+2b)=(*)2-
(7ab-zx)*(zx+7ab)=*()2-()2
(7z+a)*(a-7z)=2-*2
(mlu+7k)*(7k-mlu)=*2-()2
(3bc3-7x)*(7x+3bc3)=*b2c6-*2
(3bc3-7x)*(7x+3bc3)=(*bc3)2-*2