a2-b2=(a-b)(a+b)
(3-x)*(3+x)=-2
(a-3)*(a+3)=2-
(3-cd)*(3+cd)=-()2
(3b-3)*(3b+3)=*2-
(3b-3)*(3b+3)=(*)2-
(1-m)*(1+m)=-2
(z-1)*(z+1)=2-
(1-cd)*(cd+1)=-()2
(3b-1)*(3b+1)=*2-
(3b-1)*(1+3b)=(*)2-
(3ab-zx)*(zx+3ab)=*()2-()2
(3z+a)*(a-3z)=2-*2
(mlu+3k)*(3k-mlu)=*2-()2
(1bc3-3x)*(3x+1bc3)=*b2c6-*2
(1bc3-3x)*(3x+1bc3)=(*bc3)2-*2