Question:medium

\(\text{Cosech}^{-1}2+\text{Cosech}^{-1}\left(-\dfrac12\right)=\)

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Convert inverse hyperbolic functions into logarithmic form before simplification.
Updated On: Jun 17, 2026
  • \(\log\left(\dfrac{3-\sqrt5}{2}\right)\)
  • \(\log(3-\sqrt5)\)
  • \(\log\left(\dfrac{7+3\sqrt5}{2}\right)\)
  • \(\log\left(\dfrac{4\sqrt5+5}{2}\right)\)
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The Correct Option is A

Solution and Explanation

Step 1: Recall the log form.
The inverse hyperbolic cosecant is $\text{cosech}^{-1}x=\log\!\left(\dfrac1x+\sqrt{1+\dfrac{1}{x^2}}\right)$. We apply it twice.
Step 2: Evaluate the first term.
For $x=2$: $\text{cosech}^{-1}2=\log\!\left(\dfrac12+\sqrt{1+\dfrac14}\right)=\log\!\left(\dfrac{1+\sqrt5}{2}\right)$.
Step 3: Evaluate the second term.
For $x=-\dfrac12$: $\text{cosech}^{-1}\!\left(-\dfrac12\right)=\log\!\left(-2+\sqrt5\right)$.
Step 4: Add the two logs.
A sum of logs is the log of the product: $\log\!\left[\dfrac{(1+\sqrt5)(\sqrt5-2)}{2}\right]$.
Step 5: Multiply the bracket.
Expand $(1+\sqrt5)(\sqrt5-2)=\sqrt5-2+5-2\sqrt5=3-\sqrt5$.
Step 6: Write the result.
So the sum is $\log\!\left(\dfrac{3-\sqrt5}{2}\right)$. \[ \boxed{\log\left(\frac{3-\sqrt5}{2}\right)} \]
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