Recall the definition: Let $\theta$ be an angle in standard position. Its reference angle is the acute angle $\theta'$ formed by the terminal side of $\theta$ and the horizontal axis.
Below, express $\theta'$ in the same units (degrees or radians) as $\theta$. You can enter arithmetic expressions like 210-180 or 3.5-pi.
The reference angle of $100^\circ$ is ${}^\circ$.
The reference angle of $350^\circ$ is ${}^\circ$.
The reference angle of $4$ is .
Hint: Draw the angle. The Figures on page 314 of the textbook may be helpful