Space geometry problems in senior two.

Draw a picture yourself and compare it with my proof. Counterevidence: suppose that H is the center of △PBC, then CH⊥PB, and because A is photographed as H in the plane PBC, so AH⊥PB, so PB⊥ plane HAC, so PB⊥AC, and because PA⊥ plane ABC, so PA ⊥.

Comments: The condition "△ABC is positive △" in this question is a bit redundant, which can be changed to "the angle cab is not right angle".