JEE Main 2021 · MathsNumerical answerNumerical valueEasyCalculation

JEE Main 26 August 2021, Shift 2, Maths Q87

Question 87 of 90 in this shift, Maths question 27 of 30, Section B.

If the projection of the vector

\hat{i}+2\hat{j}+\hat{k}

on the sum of the two vectors

2\hat{i}+4\hat{j}-5\hat{k}

and

-\lambda\hat{i}+2\hat{j}+3\hat{k}

is 1, then

\lambda

is equal to __________.

Official answer

NTA final key.

Chapter: Vector Algebra
Topic: Dot Product
Idea tested: Scalar and Vector Projection

Same idea in other shifts

Asked 11× in all

2 Apr 2025, Shift 1 · Q11If $\vec{a}$ is a nonzero vector such that its projections on the vectors $2\hat{i}-\hat{j}+2\hat{k}$ , $\hat{i}+2\hat{j}-2\hat{k}$ and…MediumSingle correct
8 Apr 2024, Shift 2 · Q18Let $\vec{a} = \hat{i} + 2\hat{j} + 3\hat{k}$ , $\vec{b} = 2\hat{i} + 3\hat{j} - 5\hat{k}$ and…MediumSingle correct
1 Feb 2024, Shift 2 · Q17Consider a $\Delta ABC$ where $A(1,3,2)$ , $B(-2,8,0)$ and $C(3,6,7)$ . If the angle bisector of $\angle BAC$ meets the line $BC$ at $D$ ,…MediumSingle correct
25 Jul 2022, Shift 2 · Q17Let $\vec{a}=\hat{i}-\hat{j}+2\hat{k}$ and let $\vec{b}$ be a vector such that $\vec{a}\times\vec{b}=2\hat{i}-\hat{k}$ and…MediumSingle correct
30 Jul 2022, Shift 2 · Q88Let $OABC$ be a parallelogram, $O$ be the origin, $A\,(2, 4, -5)$ and $C\,(b, 2, 3)$ . If $P\,(a, a, a)$ and $Q\,(9-a^2, 3, a-1)$ ,…HardNumerical value
26 Jun 2022, Shift 2 · Q16Let $\vec{a} = \hat{i} + \hat{j} + 2\hat{k}$ , $\vec{b} = 2\hat{i} - 3\hat{j} + \hat{k}$ and $\vec{c} = \hat{i} - \hat{j} + \hat{k}$ be…MediumSingle correct
29 Jun 2022, Shift 1 · Q5Let $\vec{a} = \alpha\hat{i} + 3\hat{j} - \hat{k}$ , $\vec{b} = 3\hat{i} - \beta\hat{j} + 4\hat{k}$ and…MediumSingle correct
17 Mar 2021, Shift 2 · Q89Let $\overrightarrow{x}$ be a vector in the plane containing vectors $\overrightarrow{a}=2\hat{i}-\hat{j}+\hat{k}$ and…HardNumerical 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.