let's recall that there are 180° in π radians, thus
[tex]\bf \begin{array}{ccll} degrees&radians\\ \cline{1-2} 180&\pi \\ -36&x \end{array}\implies \cfrac{180}{-36}=\cfrac{\pi }{x}\implies -5=\cfrac{\pi }{x}\implies x=\cfrac{\pi }{-5}\implies x=-\cfrac{\pi }{5}[/tex]
