a2-b2=(a-b)(a+b)
(4-x)*(4+x)=-2
(a-4)*(a+4)=2-
(4-cd)*(4+cd)=-()2
(3b-4)*(3b+4)=*2-
(3b-4)*(3b+4)=(*)2-
(16-m)*(16+m)=-2
(z-16)*(z+16)=2-
(16-cd)*(cd+16)=-()2
(4b-16)*(4b+16)=*2-
(4b-16)*(16+4b)=(*)2-
(3ab-zx)*(zx+3ab)=*()2-()2
(3z+a)*(a-3z)=2-*2
(mlu+3k)*(3k-mlu)=*2-()2
(16bc3-3x)*(3x+16bc3)=*b2c6-*2
(16bc3-3x)*(3x+16bc3)=(*bc3)2-*2