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