Evaluate the integral by completing the square and using triponometric sobstitution.

${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{dx}{\sqrt[\phantom{2}]{7x-x^2}}$

$($Express mumbers in exact form. Use symbolic nocasion and fractions where needed. Use C for the arbitrary coestant Ahorrb into $C$ as mach as possible.$)$

${\displaystyle \underset{\phantom{}}{\overset{\phantom{}}{}}}\frac{dx}{\sqrt[\phantom{2}]{7x-x^2}}=$

$$