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If Tan−1 3 + Tan−1 X = Tan−1 8, Then X = (A) 5 (B) 1/5 (C) 5/14 (D) 14/5 - Mathematics

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Question

If tan−1 3 + tan−1 x = tan−1 8, then x =

Options

  • 5

  • 1/5

  • 5/14

  • 14/5

MCQ
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Solution

(b) `1/5`

We know that 
\[\tan^{- 1} x + \tan^{- 1} y = \tan^{- 1} \frac{x + y}{1 - xy}\]
Now,
\[\tan^{- 1} 3 + \tan^{- 1} x = \tan^{- 1} 8\]
\[ \Rightarrow \tan^{- 1} \left( \frac{3 + x}{1 - 3x} \right) = \tan^{- 1} 8\]
\[ \Rightarrow \frac{3 + x}{1 - 3x} = 8\]
\[ \Rightarrow 3 + x = 8 - 24x\]
\[ \Rightarrow 3 - 8 = - 24x - x\]
\[ \Rightarrow - 5 = - 25x\]
\[ \Rightarrow x = \frac{5}{25} = \frac{1}{5}\]
\[\]

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Chapter 4: Inverse Trigonometric Functions - Exercise 4.16 [Page 121]

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RD Sharma Mathematics [English] Class 12
Chapter 4 Inverse Trigonometric Functions
Exercise 4.16 | Q 18 | Page 121

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