now, if you recall, there are 180° in π radians, now, so how many radians in 1°?
[tex]\bf \begin{array}{ccll}
de grees&radians\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
180&\pi \\
1&r
\end{array}\implies \cfrac{180}{1}=\cfrac{\pi }{r}\implies r=\cfrac{1\cdot \pi }{180}[/tex]
