(16) Let $P$ be any point on the ellipse $\frac{x^{2}}{16}+\frac{y^{2}}{9}=1$ other than the endpoints of the major axis, $F_{1}$ and $F_{2}$ be its left and right foci, and $O$ be the center. Then $\left|P F_{1}\right| \cdot\left|P F_{2}\right|+|O P|^{2}=$ $\qquad$
(16) 25 Hint: By the definition of an ellipse and the cosine rule, the solution can be found.