This is not to prepare any thing essential for any exam, but this will explain to audience the reason why we have to use radians? - why radians?
Well... the simple answer is radians is reality and degrees/gradians is... fake. haha
Take into account a circle. What is so special about it? Well a circle has its uniqueness that when you draw a curve it ends up where it started and that there is a point in the centre from which all distances on the circle are same.