∫∠PBP' = 60 degrees
∴δbpp' is equilateral,
∴PP'=PB=4
∫ 3 2+4 2 = 5 2, that is, PA 2+PP' 2 = P 'a 2.
∴∠APP'=90 degree
∠APB=90+60= 150。
(Not the size of ∠PAB)