For mathematics and physics, we rarely use degrees as arguments of the trigonometric functions but radians. The radian measure of an angle is defined to be the ratio of the subtended arc to the radius of the circle or . Another way of saying this is that the radian measure of an angle tells how many times the circle's radius is contained in the length of the arc which is cut off by the terminal side of the angle.  The radian measure of an angle will be one if the length of the arc is equal to the length of the radius.

If you straighten the arc

length, it will be the same

length as the radius.

Here, if you straighten

the arc length, it would be

as long as the diameter of

the circle.

Notice here the arc

length associated with 3

radians is almost a semi-

circle. When q = p

radians or about 3.14

radians, then the arc would

be a semicircle.

For more practilce check out these fun activities: