Another question where the solution literally went over my head. need help in understanding this

I tried following the approach but my god the solution is so complex.
Please break it down on how to approach it.


How would you approach it?

I wanted to know how 60 degree was root 3/2.
I am not able to understand it at all

We have a 30-60-90 triangle. There is a common relationship between the sides that we expect students to memorise (or deduce it from other ways such as by using trigonometry). What is it?