giúp mik ms ạ mik cảm ơn

`~rai~`

\(6A.\\a)25^{n+1}-25^n\\=25^n.25-25^n\\=25^n.(25-1)\\=25^n.24\\=25^{n-1}.(25.24)\\=25^{n-1}.600\\=25^{n-1}.6.100\quad \vdots 100\quad\forall x\in\mathbb{N}\\\Rightarrow 25^{n+1}-25^n\quad\vdots 100\quad\forall x\in\mathbb{N}.(đpcm)\\b)n^2(n-1)-2n(n-1)\\=(n-1)(n^2-2n)\\=n(n-1)(n-2)\\\text{Vì tích 3 số nguyên liên tiếp luôn chia hết cho 6}\\\Rightarrow n(n-1)(n-2)\quad\vdots 6\quad\forall x\in\mathbb{Z}\\\Rightarrow n^2(n-1)-2n(n-1)\quad\vdots 6\quad\forall x\in\mathbb{Z}.(đpcm)\\6B.\\a)50^{n+2}-50^{n+1}\\=50^n.50^2-50^n.50\\=50^n.(50^2-50)\\=50^n.2450\\=50^n.10.245\quad\vdots 245\quad\forall x\in\mathbb{N}.\\\Rightarrow 50^{n+2}-50^{n+1}\quad\vdots 245\quad\forall x\in\mathbb{N}.(đpcm)\\b)n^3-n\\=n(n^2-1)\\=n(n-1)(n+1)\\\text{Vì tích 3 số nguyên liên tiếp luôn chi hết cho 6}\\\Rightarrow n(n-1)(n+1)\quad\vdots6\quad\forall x\in\mathbb{Z}\\\Rightarrow n^3-n\quad\vdots 6\quad\forall x\in\mathbb{Z}.(đpcm)\)