Concept:
If \( \theta = \sin^{-1}(x) \), then \( \sin \theta = x \) and \( \theta \in \left[-\frac{\pi}{2}, \frac{\pi}{2}\right] \).
Step 1: Let the angle be \( \theta \).
\[
\theta = \sin^{-1}\left(\frac{-1}{\sqrt{2}}\right)
\Rightarrow \sin \theta = -\frac{1}{\sqrt{2}}
\]
Step 2: Find \( \theta \).
We know:
\[
\sin\left(-\frac{\pi}{4}\right) = -\frac{1}{\sqrt{2}}
\]
Since principal value lies in \( \left[-\frac{\pi}{2}, \frac{\pi}{2}\right] \),
\[
\theta = -\frac{\pi}{4}
\]
Step 3: Find tangent.
\[
\tan \theta = \tan\left(-\frac{\pi}{4}\right) = -1
\]