Answer
$\theta_1 = 48.76^{\circ}$
Work Step by Step
$\frac{c_1}{c_2} = \frac{sin~\theta_1}{sin~\theta_2}$
If $\theta_2 = 90^{\circ}$, then $sin~\theta_2 = 1$
We can find the value of $\theta_1$:
$\frac{c_1}{c_2} = \frac{sin~\theta_1}{sin~\theta_2}$
$0.752 = \frac{sin~\theta_1}{1}$
$\theta_1 = arcsin(0.752)$
$\theta_1 = 48.76^{\circ}$
