a2-b2=(a-b)(a+b)
(3-x)*(3+x)=-2
(a-3)*(a+3)=2-
(3-cd)*(3+cd)=-()2
(2b-3)*(2b+3)=*2-
(2b-3)*(2b+3)=(*)2-
(9-m)*(9+m)=-2
(z-9)*(z+9)=2-
(9-cd)*(cd+9)=-()2
(3b-9)*(3b+9)=*2-
(3b-9)*(9+3b)=(*)2-
(2ab-zx)*(zx+2ab)=*()2-()2
(2z+a)*(a-2z)=2-*2
(mlu+2k)*(2k-mlu)=*2-()2
(9bc3-2x)*(2x+9bc3)=*b2c6-*2
(9bc3-2x)*(2x+9bc3)=(*bc3)2-*2