Answer
28 degrees
Work Step by Step
Let the initial intensity of the plane-polarized light be $I_o$.
Use Eq. 24–5 twice.
$$I_1=I_ocos^2\theta_1$$
$$I_2=I_1cos^2\theta_2= I_o (cos^2 \theta_1)(cos^2 48^{\circ})=0.35I_o$$
$$\theta_1=cos^{-1}(\frac{\sqrt{0.35}}{cos48^{\circ}})= 28^{\circ} $$
