we know that there are 180° in π radians, so how many radians are there in 126°?
[tex] \bf \begin{array}{ccll}
degrees&radians\\
\text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\
180&\pi \\
126&x
\end{array}\implies \cfrac{180}{126}=\cfrac{\pi }{x}\implies x=\cfrac{126\pi }{180}\implies \stackrel{simplified}{x=\cfrac{7\pi }{10}} [/tex]
