Question

how to find exact value of sin (60 degrees)?

Answer 1

Let's draw out the angle on a graph with the values of the triangle it creates.
The sin of any angle is the side opposite the angle over the hypotenuse. So the sin of 60 is \[\frac{ \sqrt{3} }{ 2 }\]See that?

Answer 2

how do you get the values for the side of the triangle?