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