a2-b2=(a-b)(a+b)
(6-x)*(6+x)=-2
(a-6)*(a+6)=2-
(6-cd)*(6+cd)=-()2
(3b-6)*(3b+6)=*2-
(3b-6)*(3b+6)=(*)2-
(19-m)*(19+m)=-2
(z-19)*(z+19)=2-
(19-cd)*(cd+19)=-()2
(6b-19)*(6b+19)=*2-
(6b-19)*(19+6b)=(*)2-
(3ab-zx)*(zx+3ab)=*()2-()2
(3z+a)*(a-3z)=2-*2
(mlu+3k)*(3k-mlu)=*2-()2
(19bc3-3x)*(3x+19bc3)=*b2c6-*2
(19bc3-3x)*(3x+19bc3)=(*bc3)2-*2