a2-b2=(a-b)(a+b)
(3-x)*(3+x)=-
2
(a-3)*(a+3)=2-
(3-cd)*(3+cd)=-(
)2
(9b-3)*(9b+3)=*
2-
(9b-3)*(9b+3)=(*
)2-
(3-m)*(3+m)=-
2
(z-3)*(z+3)=2-
(3-cd)*(cd+3)=-(
)2
(3b-3)*(3b+3)=*
2-
(3b-3)*(3+3b)=(*
)2-
(9ab-zx)*(zx+9ab)=*(
)2-(
)2
(9z+a)*(a-9z)=2-
*
2
(mlu+9k)*(9k-mlu)=*
2-(
)2
(3bc3-9x)*(9x+3bc3)=*b2c6-
*
2
(3bc3-9x)*(9x+3bc3)=(*bc3)2-
*
2