##arcsin(sqrt(3)/2)=60=pi/3##

##sqrt(3)/2## is a known value and the main angle ##alpha## that has ##sin(alpha)=sqrt(3)/2## is ##alpha=60=pi/3##.

Because arcsin is a function ##RR->[-1;1]## we take only the value ##alpha=pi/3## without the periodic values.

So ##arcsin(sqrt(3)/2)=60=pi/3##.