\(B=\left(\dfrac{x}{x^2-25}-\dfrac{x-5}{x^2+5x}\right):\dfrac{2x-5}{x^2+5x}+\dfrac{x}{5-x}\) (1).
Đkxđ: \(x\ne\pm5;\)
(1) \(=\left(\dfrac{x}{\left(x+5\right)\left(x-5\right)}-\dfrac{x-5}{x\left(x+5\right)}\right):\dfrac{2x-5}{x\left(x+5\right)}+\dfrac{x}{5-x}\)
\(=\left(\dfrac{x^2-\left(x-5\right)\left(x-5\right)}{x\left(x+5\right)\left(x-5\right)}\right):\dfrac{2x-5}{x\left(x+5\right)}+\dfrac{x}{5-x}\)
\(=\dfrac{25}{x\left(x+5\right)\left(x-5\right)}.\dfrac{x\left(x+5\right)}{2x-5}-\dfrac{x}{x-5}\)
\(=\dfrac{25}{\left(x-5\right)\left(2x-5\right)}-\dfrac{x}{x-5}\)
\(=\dfrac{25-x\left(2x-5\right)}{\left(x-5\right)\left(2x-5\right)}\)
\(=\dfrac{25-2x^2+5x}{\left(x-5\right)\left(2x-5\right)}\)
