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Write the Value of Sin−1 \[\Left( \Cos\Frac{\Pi}{9} \Right)\] - Mathematics

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Question

Write the value of sin−1 \[\left( \cos\frac{\pi}{9} \right)\]

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Solution

Consider,
\[\sin^{- 1} \left( \cos\frac{\pi}{9} \right) = \sin^{- 1} \left\{ \sin\left( \frac{\pi}{2} - \frac{\pi}{9} \right) \right\} \left[ \because \cos x = \sin\left( \frac{\pi}{2} - x \right) \right]\]
\[ = \sin^{- 1} \left\{ \sin\left( \frac{7\pi}{18} \right) \right\}\]
\[ = \frac{7\pi}{18} \left[ \because \sin^{- 1} \left( \sin{x} \right) = x \right]\]
∴ \[\sin^{- 1} \left( \cos\frac{\pi}{9} \right) = \frac{7\pi}{18}\]

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Chapter 4: Inverse Trigonometric Functions - Exercise 4.15 [Page 117]

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RD Sharma Mathematics [English] Class 12
Chapter 4 Inverse Trigonometric Functions
Exercise 4.15 | Q 25 | Page 117

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