Gujarat BoardEnglish MediumSTD 12 ScienceMathsInverse Trigonometric Functions1 Mark
Question
Find the principal value of cosec-1$(-\sqrt{2})$.
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Answer
Let cosec-1 $(-\sqrt{2})=y$. Then, cosec y = $-\sqrt{2}=-cosec \left(\frac{\pi}{4}\right)=cosec \left(-\frac{\pi}{4}\right)$. We know that the range of the principal value branch of cosec-1 is $\left[-\frac{\pi}{2}, \frac{\pi}{2}\right]-\{0\}$ and $cosec \left(-\frac{\pi}{4}\right)=-\sqrt{2}$. Therefore, the principal value of cosec-1$(-\sqrt{2})$ is $-\frac{\pi}{4}$.
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