Remember that
[tex]360^o=2\pi[/tex]so
Applying proportion
Find out how many radians represent 405 degrees
[tex]\begin{gathered} \frac{2\pi}{360^o}=\frac{x}{405^o} \\ solve\text{ for x} \\ x=\frac{2\pi}{360^{o}}*405^o \\ \\ x=\frac{810\pi}{360} \\ \\ x=\frac{9\pi}{4}\text{ radians} \end{gathered}[/tex]