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-
(1-m)*(1+m)=-
2
(z-1)*(z+1)=2-
(1-cd)*(cd+1)=-(
)2
(4b-1)*(4b+1)=*
2-
(4b-1)*(1+4b)=(*
)2-
(2ab-zx)*(zx+2ab)=*(
)2-(
)2
(2z+a)*(a-2z)=2-
*
2
(mlu+2k)*(2k-mlu)=*
2-(
)2
(1bc3-2x)*(2x+1bc3)=*b2c6-
*
2
(1bc3-2x)*(2x+1bc3)=(*bc3)2-
*
2