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JEE Main 20265 AprilMorning Shift
Exam
JEE Main
Year
2026
Date
5 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Inverse Trigonometric Functions

JEE Main 2026 · 5 April · Morning Shift · Mathematics · Inverse Trigonometric Functions

If (π)/(4) + ∑_ p=1 ^ 11 ^ -1 ( 2^ p-1 1 + 2^ 2p-1 ) = α , then α...

If π4+∑p=111tan⁡−1(2p−11+22p−1)=α\dfrac{\pi}{4} + \displaystyle\sum_{p=1}^{11} \tan^{-1}\left(\dfrac{2^{p-1}}{1 + 2^{2p-1}}\right) = \alpha, then tan⁡α\tan\alpha is equal to __________.

Correct answer

0

Step-by-step solution

The general term of the given series is Tp=tan⁡−1(2p−11+22p−1)T_p = \tan^{-1}\left(\dfrac{2^{p-1}}{1 + 2^{2p-1}}\right).

This can be rewritten by expressing the numerator and denominator in terms of 2p2^p and 2p−12^{p-1}:

Tp=tan⁡−1(2p−2p−11+2p⋅2p−1)T_p = \tan^{-1}\left(\dfrac{2^p - 2^{p-1}}{1 + 2^p \cdot 2^{p-1}}\right)

Using the inverse trigonometric identity tan⁡−1(x−y1+xy)=tan⁡−1x−tan⁡−1y\tan^{-1}\left(\dfrac{x - y}{1 + xy}\right) = \tan^{-1}x - \tan^{-1}y, we get:

Tp=tan⁡−1(2p)−tan⁡−1(2p−1)T_p = \tan^{-1}(2^p) - \tan^{-1}(2^{p-1})

Summing TpT_p from p=1p = 1 to 1111 gives a telescoping series:

∑p=111Tp=(tan⁡−1(21)−tan⁡−1(20))+(tan⁡−1(22)−tan⁡−1(21))+⋯+(tan⁡−1(211)−tan⁡−1(210))\displaystyle\sum_{p=1}^{11} T_p = \left(\tan^{-1}(2^1) - \tan^{-1}(2^0)\right) + \left(\tan^{-1}(2^2) - \tan^{-1}(2^1)\right) + \dots + \left(\tan^{-1}(2^{11}) - \tan^{-1}(2^{10})\right)

Canceling the intermediate terms, we obtain:

∑p=111Tp=tan⁡−1(211)−tan⁡−1(20)\displaystyle\sum_{p=1}^{11} T_p = \tan^{-1}(2^{11}) - \tan^{-1}(2^0)

Since 20=12^0 = 1 and tan⁡−1(1)=π4\tan^{-1}(1) = \dfrac{\pi}{4}, the sum becomes:

∑p=111Tp=tan⁡−1(211)−π4\displaystyle\sum_{p=1}^{11} T_p = \tan^{-1}(2^{11}) - \dfrac{\pi}{4}

Substituting this back into the expression for α\alpha:

α=π4+tan⁡−1(211)−π4\alpha = \dfrac{\pi}{4} + \tan^{-1}(2^{11}) - \dfrac{\pi}{4}

α=tan⁡−1(211)\alpha = \tan^{-1}(2^{11})

Taking the tangent of both sides, we get:

tan⁡α=211=2048\tan\alpha = 2^{11} = 2048

Answer: 20482048
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