[tex]\bf \begin{cases}
g(x)=\cfrac{5-x}{2x-1}\\\\
f(x)=\cfrac{x+5}{2x+1}
\end{cases}\qquad g(~~f(x)~~)=\cfrac{5-f(x)}{2[f(x)]+1}
\\\\\\
g(~~f(x)~~)=\cfrac{5-\left(\frac{x+5}{2x+1} \right)}{2\left(\frac{x+5}{2x+1} \right)-1}\implies g(~~f(x)~~)=\cfrac{\frac{5(2x+1)-(x+5)}{2x+1}}{\frac{2x+10}{2x+1}-1}[/tex]
[tex]\bf g(~~f(x)~~)=\cfrac{\frac{10x+5-x-5}{2x+1}}{\frac{2x+10-1(2x+1)}{2x+1}}\implies
g(~~f(x)~~)=\cfrac{\frac{9x}{2x+1}}{\frac{2x+10-2x-1}{2x+1}}
\\\\\\
g(~~f(x)~~)=\cfrac{\frac{9x}{2x+1}}{\frac{9}{2x+1}}\implies g(~~f(x)~~)=\cfrac{\underline{9} x}{\underline{2x+1}}\cdot \cfrac{\underline{2x+1}}{\underline{9}}
\\\\\\
g(~~f(x)~~)=x[/tex]
