If you have learned geometry in junior high school, this problem should not be difficult (reflection angle = incident angle). Anyone who can play golf knows this truth. Let's analyze it with you now. First of all, we know that the angle of point E is 90 degrees, which is certain, so BAE+ABE=90 degrees, because (reflection angle = incident angle) BAE=PAD, ABE=FBC, so PAD+FBC=90 degrees. If you don't understand, design a degree on the corner of the PAD yourself, and then calculate the degree according to my formula and experience it.