alleryThe value of $\cos^{-1}(-1)$ is:
A$0$, since $\cos 0 = 1$ but we want $-1$ on chart
B$\pi$, since $\cos\pi = -1$ in the principal range
C$-\pi$, taking a negative angle on the chart instead
D$\pi/2$, the angle whose cosine is $0$ on the chart
Answer & 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 $\cos^{-1}$.
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