What is Radian?

In higher classes, we don’t use degree to measure angles

We use radians.

We define radian in terms of length of arc :

Angle subtended by an arc of 1 unit in a circle of radius 1 unit is 1 radian .

In other words,

• If length of arc is 1 unit
• & Radius = 1 unit
• Then, angle at center = 1 radian

Note: In θ = l/r i.e. length of arc formula,

Angle is measured in radians