Giúp em giải bài tập với ạ

Giải thích các bước giải:

a.Khi $x=2$

$\to A=\dfrac{2^2-2}{2\cdot 2+1} =\dfrac25$

b.Ta có:

$B=\dfrac1{x-1}+\dfrac{x}{x^2-1}$

$\to B=\dfrac{x+1}{\left(x-1\right)\left(x+1\right)}+\dfrac{x}{\left(x-1\right)\left(x+1\right)}$

$\to B=\dfrac{x+1+x}{\left(x-1\right)\left(x+1\right)}$

$\to B=\dfrac{2x+1}{\left(x-1\right)\left(x+1\right)}$

$\to P=\dfrac{x^2-x}{2x+1}\cdot \dfrac{2x+1}{\left(x-1\right)\left(x+1\right)}$

$\to P=\dfrac{x(x-1)}{2x+1}\cdot \dfrac{2x+1}{\left(x-1\right)\left(x+1\right)}$

$\to P=\dfrac{x}{x+1}$

c.Để $3P\in Z$

$\to \dfrac{3x}{x+1}\in Z$

$\to 3x\quad\vdots\quad x+1$

$\to 3x+3-3\quad\vdots\quad x+1$

$\to 3(x+1)-3\quad\vdots\quad x+1$

$\to 3\quad\vdots\quad x+1$

$\to x+1\in U(3)$

$\to x+1\in\{1, 3, -1, -3\}$

$\to x\in\{0, 2, -2, -4\}$