what is radian?
how to use it? can you explain by using examples?
i know a formula related to radian : s= r(theta)
why it is better to use the formula to find length of arc rather than formula : (angle at the center)/360 times circumference ?
Radians measure angles. The measure is the length of the arc of a unit circle subtended by the angle at the centre of the circle.
It is a better measure than degrees for many purposes because it is a natural unit (unlike the degree which is a 90-th part of a right angle). Which results in better properties for trig (and related) functions when expressed in radians compared to when expressed in degrees.
RonL
Just restating what capt. said.
Radians are a different way to measure degrees, instead of a right angle being $\displaystyle 90^o$ in radians it's $\displaystyle \frac{\pi}{2}$
it's more useful to use radians in certain situations (it's like using kilometres instead of miles, it's easier to work with)