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