Vector Algebra

Two vectors \({\overrightarrow P }\) and \({\overrightarrow Q }\) have equal magnitudes. If the magnitude of \({\overrightarrow P + \overrightarrow Q }\) is n times the magnitude of \({\overrightarrow P - \overrightarrow Q }\), then angle between \({\overrightarrow P }\) and \({\overrightarrow Q }\) is :