请解答图中的题目---第四题:
已知: △ABC 是正三角形, P 是三角形内一点, PA = 3, PB = 4, PC = 5. 求: ∠APB 的度数.
Chart/Diagram Description:
* Type: Geometric figure (Triangle with an internal point).
* Main Elements:
* A triangle labeled ABC.
* An internal point labeled P.
* Line segments connecting P to the vertices A, B, and C (PA, PB, PC).
* Line segments forming the sides of the triangle (AB, BC, CA).
* Labels: A, B, C at the vertices of the triangle; P inside the triangle.
* Relative Position and Direction: P is located within the triangle ABC. Lines PA, PB, PC connect P to A, B, C respectively.