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Saturday, 31 October

JEE Main 2021 · MathsMultiple choiceSingle correctMediumMulti-step

JEE Main 17 March 2021, Shift 1, Maths Q68

Question 68 of 90 in this shift, Maths question 8 of 30, Section A.

If cot⁡−1(α)=cot⁡−12+cot⁡−18+cot⁡−118+cot⁡−132+.....\cot^{-1}(\alpha)=\cot^{-1}2+\cot^{-1}8+\cot^{-1}18+\cot^{-1}32+..... upto 100 terms, then α\alpha is :
  1. (1)1.00
  2. (2)1.01Official answer
  3. (3)1.02
  4. (4)1.03

Official answer

Option 2

NTA final key.

Chapter
Inverse Trigonometric Functions
Topic
Inverse Trig Identities
Idea tested
Telescoping Series with cot-1

Same idea in other shifts

Asked 2× in all
  1. 4 Apr 2025, Shift 2 · Q13The sum of the infinite series…HardSingle correct

Question text from the official JEE Main paper published by NTA; answer from the final answer key. Chapter, topic and idea tags, difficulty and skill are Lumi’s. Lumi analyses 108 of the 174 JEE Main shifts held from 2017 to 2026.