a2-b2=(a-b)(a+b)
(9-x)*(9+x)=-2
(a-9)*(a+9)=2-
(9-cd)*(9+cd)=-()2
(1b-9)*(1b+9)=*2-
(1b-9)*(1b+9)=(*)2-
(12-m)*(12+m)=-2
(z-12)*(z+12)=2-
(12-cd)*(cd+12)=-()2
(9b-12)*(9b+12)=*2-
(9b-12)*(12+9b)=(*)2-
(1ab-zx)*(zx+1ab)=*()2-()2
(1z+a)*(a-1z)=2-*2
(mlu+1k)*(1k-mlu)=*2-()2
(12bc3-1x)*(1x+12bc3)=*b2c6-*2
(12bc3-1x)*(1x+12bc3)=(*bc3)2-*2