we know there are 180° in π radians, how many degrees then in -3π/10 radians?
[tex]\bf \begin{array}{ccll} degrees&radians\\ \cline{1-2} 180&\pi \\\\ x&-\frac{3\pi }{10} \end{array}\implies \cfrac{180}{x}=\cfrac{\pi }{~~-\frac{3\pi }{10}~~}\implies \cfrac{180}{x}=\cfrac{\frac{\pi}{1} }{~~-\frac{3\pi }{10}~~} \\\\\\ \cfrac{180}{x}=\cfrac{\pi }{1}\cdot \cfrac{10}{-3\pi }\implies \cfrac{180}{x}=-\cfrac{10}{3}\implies 540=-10x\implies \cfrac{540}{-10}=x \\\\[-0.35em] \rule{34em}{0.25pt}\\\\ ~\hfill -54=x~\hfill[/tex]
