If \(y=\cos^{-1}x\), in which interval does (y) lie?

Correct answer: \(\left[0,\pi\right]\)

For \(y=\cos^{-1}x\), the domain is \(x\in[-1,1]\), and its principal-value range is \(\left[0,\pi\right]\). At \(x=1\), \(y=0\), while at \(x=-1\), \(y=\pi\); hence both endpoints are included. The interval \(\left(-\frac{\pi}{2},\frac{\pi}{2}\right)\) is associated with the principal range of \(\sin^{-1}x\). Exam tip: remember that \(\cos^{-1}x\) takes values from \(0\) to \(\pi\).