a2-b2=(a-b)(a+b)
(7-x)*(7+x)=-
2
(a-7)*(a+7)=2-
(7-cd)*(7+cd)=-(
)2
(6b-7)*(6b+7)=*
2-
(6b-7)*(6b+7)=(*
)2-
(16-m)*(16+m)=-
2
(z-16)*(z+16)=2-
(16-cd)*(cd+16)=-(
)2
(7b-16)*(7b+16)=*
2-
(7b-16)*(16+7b)=(*
)2-
(6ab-zx)*(zx+6ab)=*(
)2-(
)2
(6z+a)*(a-6z)=2-
*
2
(mlu+6k)*(6k-mlu)=*
2-(
)2
(16bc3-6x)*(6x+16bc3)=*b2c6-
*
2
(16bc3-6x)*(6x+16bc3)=(*bc3)2-
*
2