a: ĐKXĐ: x<>0; x<>1
b: \(A=\left(\dfrac{x}{x-1}-\dfrac{1}{x\left(x-1\right)}\right):\dfrac{\left(x+1\right)^2}{5x}\)
\(=\dfrac{x^2-1}{x\left(x-1\right)}\cdot\dfrac{5x}{\left(x+1\right)^2}=\dfrac{\left(x+1\right)\cdot5}{\left(x+1\right)^2}=\dfrac{5}{x+1}\)
c: Để A=0 thì 5=0(loại)