# How do you convert 25degrees into radian measure?

I know that 180° is $\pi$ radians (consider the length of a half circle arc; it spans an angle of 180° and its length is $\pi r$ or half the entire circle perimeter. But radians is (arc length)/(radius), so for your half circle you have that also spans $\pi \frac{r}{r} = \pi$ radians).
(180°)/(25°) must have the same result as $\frac{\pi}{x}$ where $x$ is the corresponding measure of 25° in radians:
x=(25°)/(180°)pi=5/36pi