JEE Main 2020 · MathsMultiple choiceSingle correctEasyApplication

JEE Main 9 January 2020, Shift 2, Maths Q69

Question 69 of 75 in this shift, Maths question 19 of 25, Section A.

x=\sum_{n=0}^{\infty}(-1)^n\tan^{2n}\theta

and

y=\sum_{n=0}^{\infty}\cos^{2n}\theta

, for

0<\theta<\frac{\pi}{4}

, then :

(1) $y(1+x)=1$
(2) $y(1-x)=1$ Official answer
(3) $x(1-y)=1$
(4) $x(1+y)=1$

Official answer

Option 2

NTA final key (Jan 2020).

Chapter: Sequences and Series
Topic: AP and GP
Idea tested: Infinite GP Sum

Same idea in other shifts

Asked 5× in all

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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 42 of the 174 JEE Main shifts held from 2017 to 2026.