\(\dfrac{4}{x-5}-\dfrac{1}{x+5}+\dfrac{13x-x^2}{25-x^2}=\dfrac{4x+20-x+5}{x^2-25}+\dfrac{x^2-13x}{x^2-25}\)
\(=\dfrac{3x+25+x^2-13x}{x^2-25}=\dfrac{x^2-10x+25}{\left(x-5\right)\left(x+5\right)}=\dfrac{\left(x-5\right)^2}{\left(x-5\right)\left(x+5\right)}=\dfrac{x-5}{x+5}\)