a2-b2=(a-b)(a+b)
(3-x)*(3+x)=-2
(a-3)*(a+3)=2-
(3-cd)*(3+cd)=-()2
(7b-3)*(7b+3)=*2-
(7b-3)*(7b+3)=(*)2-
(10-m)*(10+m)=-2
(z-10)*(z+10)=2-
(10-cd)*(cd+10)=-()2
(3b-10)*(3b+10)=*2-
(3b-10)*(10+3b)=(*)2-
(7ab-zx)*(zx+7ab)=*()2-()2
(7z+a)*(a-7z)=2-*2
(mlu+7k)*(7k-mlu)=*2-()2
(10bc3-7x)*(7x+10bc3)=*b2c6-*2
(10bc3-7x)*(7x+10bc3)=(*bc3)2-*2