Question

Define and explain radian !!​

Answer 1

Hi my dear friend,

a unit of angle, equal to an angle at the center of a circle whose arc is equal in length to the radius.

~Thank you

Answer 2

a unit of measurement of angles equal to about 57.3°, equivalent to the angle subtended at the centre of a circle by an arc equal in length to the radius.
The radian ( SI symbol rad ) is the SI unit for measuring angles , and is the standard unit of angular measure used in many areas of mathematics . The length of an arc of a unit circle is numerically equal to the measurement in radians of the angle that it
subtends ; one radian is just under 57.3 degrees (expansion at OEIS: A072097 ). The unit was formerly an SI supplementary unit , but this category was abolished in 1995 and the radian is now considered an
SI derived unit .