Statistical Inference — partial correlation coefficient formula

Let $r_{ij}$ denote the correlation coefficient between $X_i$ and $X_j$ variables. If $r_{12} = \sin^2\theta$, $r_{13} = \cos\theta$, $r_{23} = \sin\theta$, where $-\pi \le \theta \le \pi$, then the partial correlation coefficient $r_{12.3}$ is