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