a2-b2=(a-b)(a+b)
(5-x)*(5+x)=-
2
(a-5)*(a+5)=2-
(5-cd)*(5+cd)=-(
)2
(2b-5)*(2b+5)=*
2-
(2b-5)*(2b+5)=(*
)2-
(5-m)*(5+m)=-
2
(z-5)*(z+5)=2-
(5-cd)*(cd+5)=-(
)2
(5b-5)*(5b+5)=*
2-
(5b-5)*(5+5b)=(*
)2-
(2ab-zx)*(zx+2ab)=*(
)2-(
)2
(2z+a)*(a-2z)=2-
*
2
(mlu+2k)*(2k-mlu)=*
2-(
)2
(5bc3-2x)*(2x+5bc3)=*b2c6-
*
2
(5bc3-2x)*(2x+5bc3)=(*bc3)2-
*
2