JEE Main 2021 · MathsMultiple choiceSingle correctMediumMulti-step

JEE Main 31 August 2021, Shift 1, Maths Q65

Question 65 of 90 in this shift, Maths question 5 of 30, Section A.

Three numbers are in an increasing geometric progression with common ratio r. If the middle number is doubled, then the new numbers are in an arithmetic progression with common difference d. If the fourth term of GP is

3\mathrm{r}^2

, then

\mathrm{r}^2-\mathrm{d}

is equal to :

(1) $7-7\sqrt{3}$
(2) $7+\sqrt{3}$ Official answer
(3) $7-\sqrt{3}$
(4) $7+3\sqrt{3}$

Official answer

Option 2

NTA final key.

Chapter: Sequences and Series
Topic: AP and GP
Idea tested: GP General Term

Same idea in other shifts

Asked 15× in all

3 Apr 2025, Shift 1 · Q6Let $a_1, a_2, a_3, \ldots$ be a G.P. of increasing positive numbers. If $a_3 a_5 = 729$ and $a_2 + a_4 = \frac{111}{4}$ , then…EasySingle correct
7 Apr 2025, Shift 2 · Q7If the sum of the second, fourth and sixth terms of a G.P. of positive terms is 21 and the sum of its eighth, tenth and twelfth terms is…MediumSingle correct
4 Apr 2024, Shift 1 · Q9Let the first three terms $2$ , $p$ and $q$ , with $q \neq 2$ , of a G.P. be respectively the $7^{th}$ , $8^{th}$ and $13^{th}$ terms of an…MediumSingle correct
8 Apr 2024, Shift 2 · Q8In an increasing geometric progression of positive terms, the sum of the second and sixth terms is $\frac{70}{3}$ and the product of the…MediumSingle correct
30 Jan 2024, Shift 2 · Q6Let $a$ and $b$ be be two distinct positive real numbers. Let $11^{\mathrm{th}}$ term of a GP, whose first term is $a$ and third term is…EasySingle correct
31 Jan 2024, Shift 2 · Q7Let $2^{nd}$ , $8^{th}$ and $44^{th}$ terms of a non-constant A. P. be respectively the $1^{st}$ , $2^{nd}$ and $3^{rd}$ terms of a G. P. If…MediumSingle correct
13 Apr 2023, Shift 2 · Q8Let $a_1, a_2, a_3, \ldots$ be a G.P. of increasing positive numbers. Let the sum of its $6^{th}$ and $8^{th}$ terms be $2$ and the…MediumSingle correct
26 Jun 2022, Shift 2 · Q27If $a_1\ (> 0), a_2, a_3, a_4, a_5$ are in a G.P., $a_2 + a_4 = 2a_3 + 1$ and $3a_2 + a_3 = 2a_4$ , then $a_2 + a_4 + 2a_5$ is equal to…MediumNumerical value

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.