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← JEE Main 2026 · 5 Apr · Shift 1
MathematicsInteger+4 / -1Question 24 of 75

JEE Main 2026 · 5 Apr · Shift 1, Mathematics question 24

If π4+∑p=111tan⁡−1(2p−11+22p−1)=α\dfrac\pi4+\displaystyle\sum_{p=1}^{11}\tan^{-1}\left(\frac{2^{p-1}}{1+2^{2p-1}}\right)=\alpha, then tan⁡α\tan\alpha is equal to ________.

Answer and worked solution

Official answer: 2048

Each term.
2p−11+22p−1=2p−2p−11+2p⋅2p−1,\frac{2^{p-1}}{1+2^{2p-1}}=\frac{2^p-2^{p-1}}{1+2^p\cdot2^{p-1}},
so the term is tan⁡−12p−tan⁡−12p−1\tan^{-1}2^p-\tan^{-1}2^{p-1}.

Telescoping. The sum is tan⁡−1211−tan⁡−11=tan⁡−12048−π4\tan^{-1}2^{11}-\tan^{-1}1=\tan^{-1}2048-\tfrac\pi4, so α=tan⁡−12048\alpha=\tan^{-1}2048.

Answer: tan⁡α=2048\tan\alpha=2048