For each of the following values of sinθ, determine the measure of θ if,

/2 ≤ θ ≤ 3/2

a) 1/2

2. for $\sin(\theta) = \frac{1}{2}$

$\theta = \frac{\pi}{6}$

Look here Special Triangles

but this answer is not in the domain you require.

Use the identity $\pi -\theta$ to get your answer.