C
cuonsachthanki


Bai`1: c/m:
[tex]A=\frac{1}{(x-y)(y-z)}+\frac{1}{(y-z)(z-x)}+\frac{1}{(z-x)(x-y)}=0[/tex]
Bai`2: c/m \forall n thuộc Z:
[tex] n^2(n^2 -1)[/tex] chia hết 12
[tex]A=\frac{1}{(x-y)(y-z)}+\frac{1}{(y-z)(z-x)}+\frac{1}{(z-x)(x-y)}=0[/tex]
Bai`2: c/m \forall n thuộc Z:
[tex] n^2(n^2 -1)[/tex] chia hết 12