Cambridge AS & A Level. 2025. Mathematics (9709). May/June - Paper 1 (13) · Pure Mathematics 1 - Question 13

Three points $P$, $Q$ and $R$ have coordinates $P(-13, 5)$, $Q(5, 1)$ and $R(2, k)$, where $k$ is a constant. It is given that the angle $PRQ$ is a right angle.

**(a)** Show that one of the possible values of $k$ is 10, and find the other possible value.