a2-b2=(a-b)(a+b)
(1-x)*(1+x)=-
2
(a-1)*(a+1)=2-
(1-cd)*(1+cd)=-(
)2
(5b-1)*(5b+1)=*
2-
(5b-1)*(5b+1)=(*
)2-
(13-m)*(13+m)=-
2
(z-13)*(z+13)=2-
(13-cd)*(cd+13)=-(
)2
(1b-13)*(1b+13)=*
2-
(1b-13)*(13+1b)=(*
)2-
(5ab-zx)*(zx+5ab)=*(
)2-(
)2
(5z+a)*(a-5z)=2-
*
2
(mlu+5k)*(5k-mlu)=*
2-(
)2
(13bc3-5x)*(5x+13bc3)=*b2c6-
*
2
(13bc3-5x)*(5x+13bc3)=(*bc3)2-
*
2