Question:

Let \(x\in \mathbb{R}\) and \(|x|\lt 1\). Then \[ \tanh^{-1}x= \]

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Remember the inverse hyperbolic tangent formula: \[ \tanh^{-1}x=\frac{1}{2}\log\left(\frac{1+x}{1-x}\right),\quad |x|\lt 1. \]
Updated On: Jun 24, 2026
  • \(\frac{1}{2}\log\left(\frac{1+x}{1-x}\right)\)
  • \(\frac{1}{2}\log\left(\frac{1-x}{1+x}\right)\)
  • \(\frac{1}{2}\log\left(x+\sqrt{1-x^2}\right)\)
  • \(\frac{1}{2}\log\left(x-\sqrt{1-x^2}\right)\)
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The Correct Option is A

Solution and Explanation

Step 1: Use the standard formula.
For \(|x|\lt 1\), \[ \tanh^{-1}x=\frac{1}{2}\log\left(\frac{1+x}{1-x}\right) \]

Step 2: Match with the options.
The expression \[ \frac{1}{2}\log\left(\frac{1+x}{1-x}\right) \] matches option \((1)\).

Step 3: Final conclusion.
Therefore, \[ \boxed{\frac{1}{2}\log\left(\frac{1+x}{1-x}\right)} \]
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