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