15. Given vectors \(\vec{p}\), \(\vec{q}\), and \(\vec{r}\),
such that \(|\vec{p}| = |\vec{q}| = |\vec{r}| = 3\)
units, and \(\vec{p}\) bisects the
angle formed by \(\vec{q}\) and
\(\vec{r}\), express \(\vec{p}\) as a linear
combination of \(\vec{q}\) and \(\vec{r}\).
