a2-b2=(a-b)(a+b)
(7-x)*(7+x)=-2
(a-7)*(a+7)=2-
(7-cd)*(7+cd)=-()2
(6b-7)*(6b+7)=*2-
(6b-7)*(6b+7)=(*)2-
(9-m)*(9+m)=-2
(z-9)*(z+9)=2-
(9-cd)*(cd+9)=-()2
(7b-9)*(7b+9)=*2-
(7b-9)*(9+7b)=(*)2-
(6ab-zx)*(zx+6ab)=*()2-()2
(6z+a)*(a-6z)=2-*2
(mlu+6k)*(6k-mlu)=*2-()2
(9bc3-6x)*(6x+9bc3)=*b2c6-*2
(9bc3-6x)*(6x+9bc3)=(*bc3)2-*2