Mathematical problems, please answer and process, thank you.

Connect BD

Because PB is perpendicular to plane ABCD, BD is the photograph of PB on plane ABCD, so the angle PBD is the angle between straight line PB and plane ABCD

< p>Because the rectangle AD=3 AB=4, then BD=5

Because PD=4 PD is perpendicular to the plane ABCD, we can find BP=root 41

Then the angle PBD is the angle PBD is the cosine of the angle between straight line PB and plane ABCD, which is 5/root 41