Question

what is a radian ? what is the value of it.

Answer 1

The Radian is a angle for circular measure. If the central angle in the circle has radius of  length 1 and length of arc is 1, then the angle is 1 rad. The circumference of a circle is C=2πR, there R is the radius of a circle. If R=1, then C=2π. The angle of whole arc is 360°, so 2π=360° and 1 rad = 1/(2π) × 360° ≈ 1/(6.28) × 360° ≈ 57.3°.