a2-b2=(a-b)(a+b)
(9-x)*(9+x)=-
2
(a-9)*(a+9)=2-
(9-cd)*(9+cd)=-(
)2
(8b-9)*(8b+9)=*
2-
(8b-9)*(8b+9)=(*
)2-
(18-m)*(18+m)=-
2
(z-18)*(z+18)=2-
(18-cd)*(cd+18)=-(
)2
(9b-18)*(9b+18)=*
2-
(9b-18)*(18+9b)=(*
)2-
(8ab-zx)*(zx+8ab)=*(
)2-(
)2
(8z+a)*(a-8z)=2-
*
2
(mlu+8k)*(8k-mlu)=*
2-(
)2
(18bc3-8x)*(8x+18bc3)=*b2c6-
*
2
(18bc3-8x)*(8x+18bc3)=(*bc3)2-
*
2