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Which statement is correct about \(\cos^{-1}\left(-2\right)\)?

Answer and explanation

Correct answer: It is not defined

Direct answer: option B, it is not defined over the real numbers. For a real angle, cosine always lies between \(-1\) and 1, inclusive. Therefore the real domain of \(\cos^{-1}x\) is \([-1,1]\). Since \(-2<-1\), \(\cos^{-1}(-2)\) has no real value. A is false because the input is outside the domain. C is false: although \(\cos\pi=-1\), not \(-2\), so the value cannot be \(\pi\). D is false because \(\cos0=1\), not \(-2\). This is a domain check, so no calculation of a principal angle is possible. Memory cue: inverse sine and cosine accept only inputs from \(-1\) to 1.

Related tags

Inverse Trigonometric FunctionsDomainCommon Mistake

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