3sin(θ/2) = 3/2

3sin(θ/2) = 3/2      divide both sides by 3

sin(θ/2) = 1/2

Now the sine θ = 1/2 when θ =  pi/6 and 5pi/6

So, set θ/2 =pi/6

Multiply both sides by 2

θ = pi/3

And set θ/2 = 5pi/6

Multiply both sides by 2

θ = 10pi/6 = 5pi/3

So...our two answers are pi/3 and 5pi/3 in the given interval