## Precalculus (10th Edition)

For inverse cosine, the value of $x$ should be in the interval $-1 \leq x\leq 1$. Since $-1.6 \lt-1$, hence $\cos^{-1}{(-1.6)}$ is not defined and therefore $\cos{(\cos^{-1}{\frac{x}{y}(-1.6)}})$ is not defined.