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Saturday, 31 October

JEE Main 2025 · MathsNumerical answerNumerical valueMediumMulti-step

JEE Main 3 April 2025, Shift 1, Maths Q24

Question 24 of 75 in this shift, Maths question 24 of 25, Section B.

Let a⃗=i^+j^+k^,b⃗=3i^+2j^−k^,c⃗=λj^+μk^\vec{a} = \hat{i} + \hat{j} + \hat{k}, \vec{b} = 3\hat{i} + 2\hat{j} - \hat{k}, \vec{c} = \lambda\hat{j} + \mu\hat{k} and d^\hat{d} be a unit vector such that a⃗×d^=b⃗×d^\vec{a} \times \hat{d} = \vec{b} \times \hat{d} and c⃗⋅d^=1\vec{c}\cdot\hat{d} = 1. If c⃗\vec{c} is perpendicular to a⃗\vec{a}, then ∣3λd^+μc⃗∣2\left|3\lambda\hat{d} + \mu\vec{c}\right|^2 is equal to ______

Official answer

5

NTA final key.

Same idea in other shifts

Asked 2× in all
  1. 12 Apr 2023, Shift 1 · Q17Let λ∈Z\lambda\in\mathbb{Z}, a⃗=λi^+j^−k^\vec{a}=\lambda\hat{i}+\hat{j}-\hat{k} and b⃗=3i^−j^+2k^\vec{b}=3\hat{i}-\hat{j}+2\hat{k}. Let c⃗\vec{c} be a vector…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.