In Trigonometey, the radian measure of an angle theta is the length of an arc that subtends in a circle of radius having a formula of circumeference divided by 2xpi and that the ratio 2pi and the circumference over the radius is called tha radian measure.
We can measure angle in two form degrees or Radian.
Radian can be described as a measure of angle subtended by a circular arc. It can be defined as the ratio of the arc length subtending angle to the radius of circle.
One radian is the measure of angle subtended by by an arc that is equal to the radius of circle.
Θ = ,
where theta is the angle subtended, s is the arc length and r is the radius of circle.