a2-b2=(a-b)(a+b)
(2-x)*(2+x)=-2
(a-2)*(a+2)=2-
(2-cd)*(2+cd)=-()2
(3b-2)*(3b+2)=*2-
(3b-2)*(3b+2)=(*)2-
(13-m)*(13+m)=-2
(z-13)*(z+13)=2-
(13-cd)*(cd+13)=-()2
(2b-13)*(2b+13)=*2-
(2b-13)*(13+2b)=(*)2-
(3ab-zx)*(zx+3ab)=*()2-()2
(3z+a)*(a-3z)=2-*2
(mlu+3k)*(3k-mlu)=*2-()2
(13bc3-3x)*(3x+13bc3)=*b2c6-*2
(13bc3-3x)*(3x+13bc3)=(*bc3)2-*2