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