a2-b2=(a-b)(a+b)
(9-x)*(9+x)=-2
(a-9)*(a+9)=2-
(9-cd)*(9+cd)=-()2
(5b-9)*(5b+9)=*2-
(5b-9)*(5b+9)=(*)2-
(3-m)*(3+m)=-2
(z-3)*(z+3)=2-
(3-cd)*(cd+3)=-()2
(9b-3)*(9b+3)=*2-
(9b-3)*(3+9b)=(*)2-
(5ab-zx)*(zx+5ab)=*()2-()2
(5z+a)*(a-5z)=2-*2
(mlu+5k)*(5k-mlu)=*2-()2
(3bc3-5x)*(5x+3bc3)=*b2c6-*2
(3bc3-5x)*(5x+3bc3)=(*bc3)2-*2