If \(y=\operatorname{cosec}^{-1}(x)\) and \(\frac{d y}{d x}=\frac{-1}{|x| \sqrt{x^2-1}}\), then

If \(y=\operatorname{cosec}^{-1}(x)\) and \(\frac{d y}{d x}=\frac{-1}{|x| \sqrt{x^2-1}}\), then
  1. \(y \in\left(-\frac{\pi}{2}, 0\right)\)
  2. \(y \in\left(-\frac{\pi}{2}, 2 \pi\right)\)
  3. \(y \in\left(-\frac{\pi}{2}, 0\right) \cup\left(0, \frac{\pi}{2}\right)\)
  4. \(y \in R\)

Solution

It is given that, \(y=\operatorname{cosec}^{-1} x\) \(\text {and } \frac{d y}{d x}=\frac{-1}{|x| \sqrt{x^2-1}}\) \(\because\) Domain of \(\operatorname{cosec}^{-1} x\) is \(\left[-\frac{\pi}{2}, \frac{\pi}{2}\right]-\{0\}\) and the \(\frac{d y}{d x}\) is define for \(x \in\left(-\frac{\pi}{2}, 0\right) \cup\left(0, \frac{\pi}{2}\right)\). Because for derivatives we should exclude the end points of a internal. Hence, option (c) is correct.

Asked in: AP EAMCET 2020 (21 Sep Shift 1)

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