a2-b2=(a-b)(a+b)
(4-x)*(4+x)=-
2
(a-4)*(a+4)=2-
(4-cd)*(4+cd)=-(
)2
(5b-4)*(5b+4)=*
2-
(5b-4)*(5b+4)=(*
)2-
(6-m)*(6+m)=-
2
(z-6)*(z+6)=2-
(6-cd)*(cd+6)=-(
)2
(4b-6)*(4b+6)=*
2-
(4b-6)*(6+4b)=(*
)2-
(5ab-zx)*(zx+5ab)=*(
)2-(
)2
(5z+a)*(a-5z)=2-
*
2
(mlu+5k)*(5k-mlu)=*
2-(
)2
(6bc3-5x)*(5x+6bc3)=*b2c6-
*
2
(6bc3-5x)*(5x+6bc3)=(*bc3)2-
*
2