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Write the Value of Cos−1 - Mathematics

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Question

Write the value of cos−1 \[\left( \tan\frac{3\pi}{4} \right)\]

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Solution

We have

\[\cos^{- 1} \left( \tan\frac{3\pi}{4} \right) = \cos^{- 1} \left\{ - \tan\left( \pi - \frac{3\pi}{4} \right) \right\} \left[ \because \tan\left( \pi - x \right) = - \tan{x} \right]\]
\[ = \cos^{- 1} \left\{ \tan\left( - \frac{\pi}{4} \right) \right\}\]
\[ = \cos^{- 1} \left\{ - \tan\left( \frac{\pi}{4} \right) \right\}\]
\[ = \cos^{- 1} \left( - 1 \right)\]
\[ = \cos^{- 1} \left( cos\pi \right) \left[ \because cos\pi = - 1 \right]\]
\[ = \pi\]

∴ \[\cos^{- 1} \left( \tan\frac{3\pi}{4} \right) = \pi\]

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

APPEARS IN

RD Sharma Mathematics [English] Class 12
Chapter 4 Inverse Trigonometric Functions
Exercise 4.15 | Q 19 | Page 117

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