The value of $\cos^{-1}(-1)$ is:
- $0$, since $\cos 0 = 1$ but we want $-1$ on chart
- $\pi$, since $\cos\pi = -1$ in the principal range
- $-\pi$, taking a negative angle on the chart instead
- $\pi/2$, the angle whose cosine is $0$ on the chart
Show answer and solution
Correct answer: B. $\pi$, since $\cos\pi = -1$ in the principal range
$\cos\pi = -1$ and $\pi \in [0, \pi]$, the principal range of $\cos^{-1}$.