Methemetics

You should know that  the circumference on a circle  is  2pi r 

well

the angle in a revolution is also 2pi radians and you should know it is also 360 degrees so...

 

\(360\;\; degrees=2\pi\;\;radians\\ 180\;\; degrees=\pi\;\;radians\\ so\\ \frac{x}{180}*180\;\; degrees=\frac{x}{180} \pi\;\;radians\\ x \;\; degrees=x*\frac{\pi}{180} \;\;radians\\~\\ 330 \;\; degrees=330*\frac{\pi}{180} \;\;radians\\\)