Giải thích các bước giải:
a.Từ đề suy ra :
$A=(\dfrac{x+1}{x-1}-\dfrac{x-1}{x+1}):\dfrac{2x}{5(x-1)}$
$\to A=\dfrac{(x+1)^2-(x-1)^2}{(x+1)(x-1)}.\dfrac{5(x-1)}{2x}$
$\to A=\dfrac{(x^2+2x+1)-(x^2-2x+1)}{x+1}.\dfrac{5}{2x}$
$\to A=\dfrac{4x}{x+1}.\dfrac{5}{2x}$
$\to A=\dfrac{10}{x+1}$
b.Để $A=2\to\dfrac{10}{x+1}=2\to x+1=5\to x=4$