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Write the Principal Value of Cos − 1 ( Cos 2 π 3 ) + Sin − 1 ( Sin 2 π 3 ) - Mathematics

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Question

Write the principal value of \[\cos^{- 1} \left( \cos\frac{2\pi}{3} \right) + \sin^{- 1} \left( \sin\frac{2\pi}{3} \right)\]

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Solution

\[\text{We have}, \cos^{- 1} \left( \cos\frac{2\pi}{3} \right) + \sin^{- 1} \left( \sin\frac{2\pi}{3} \right) = \cos^{- 1} \left( \cos\frac{2\pi}{3} \right) + \sin^{- 1} \left\{ \sin\left( \pi - \frac{\pi}{3} \right) \right\} \left[ \because \left( \pi - \frac{2\pi}{3} \right) \in \left[ - \frac{\pi}{2}, \frac{\pi}{2} \right] \right]\]
\[ = \cos^{- 1} \left( \cos\frac{2\pi}{3} \right) + \sin^{- 1} \left\{ \sin\left( \frac{\pi}{3} \right) \right\}\]
\[ = \frac{2\pi}{3} + \frac{\pi}{3}\]
\[ = \pi\]
∴ \[\cos^{- 1} \left( \cos\frac{2\pi}{3} \right) + \sin^{- 1} \left( \sin\frac{2\pi}{3} \right) = \pi\]

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Chapter 4: Inverse Trigonometric Functions - Exercise 4.15 [Page 118]

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RD Sharma Mathematics [English] Class 12
Chapter 4 Inverse Trigonometric Functions
Exercise 4.15 | Q 40 | Page 118

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