Radian
/ˈreɪdiən/
Definition 1 of 1
Pro Tip 1/3Visualize the Circle
Imagine wrapping a circle's radius along its edge to see the radian angle it creates. 
If you visualize a pizza slice, one radian would be a slice where the crust's arc is equal to the radius of the pizza.
Pro Tip 2/3Conversion Relation
Understand the conversion between radians and degrees, since 180 degrees is equal to π radians. 
To find an angle in radians, divide the degrees by 180 and multiply by π.
Pro Tip 3/3Radians in Formulas
Know that radians are used in mathematical expressions involving trigonometry and calculus. The formula for the area of a sector is (1/2)*r^2*θ, where θ is the angle in radians.