Question:hard

If \(\int (\sqrt{\tan x}+\sqrt{\cot x})dx=a\tan ^{-1}\left(\frac{\tan x-1}{\sqrt{b\tan x}}\right)+c\), for \(x\in \left(0,\frac{\pi }{2}\right)\), then \(a^{10}+b^{5}=\cdots\)

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Substitute u equal to the square root of tan x and reduce to a standard form using u minus 1 over u.
Updated On: Nov 12, 2026
  • \(16\)
  • \(64\)
  • \(36\)
  • \(100\)
Show Solution

The Correct Option is B

Solution and Explanation

Step 1: Plan
Differentiate the given form with $t=\tan x$ and match it with the integrand $\dfrac{t+1}{\sqrt t}$.

Step 2: Differentiate
Let $w=\dfrac{t-1}{\sqrt{bt}}$. Then $\dfrac{dw}{dx}=\dfrac{1}{2\sqrt b}\cdot\dfrac{(t+1)(1+t^{2})}{t^{3/2}}$ and $1+w^{2}=\dfrac{bt+(t-1)^{2}}{bt}$.\nFor $b=2$, $1+w^{2}=\dfrac{t^{2}+1}{2t}$.

Step 3: Match
Then $\dfrac{d}{dx}\left[a\tan^{-1}w\right]=\dfrac{a}{\sqrt2}\cdot\dfrac{t+1}{\sqrt t}$.\nThis equals $\dfrac{t+1}{\sqrt t}$ only when $a=\sqrt2$ with $b=2$.

Step 4: Compute
$a^{10}=(\sqrt2)^{10}=32$ and $b^{5}=2^{5}=32$, so the sum is $64$.

Final Answer:
With a equal to root 2 and b equal to 2 the sum is 64. \[ \boxed{\text{(B) }64} \]
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