JEE Main 2021 · MathsMultiple choiceSingle correctEasyCalculation

JEE Main 25 July 2021, Shift 2, Maths Q78

Question 78 of 90 in this shift, Maths question 18 of 30, Section A.

|\vec{a}|=2

|\vec{b}|=5

and

|\vec{a}\times\vec{b}|=8

, then

|\vec{a}\cdot\vec{b}|

is equal to :

(1) $4$
(2) $5$
(3) $3$
(4) $6$ Official answer

Official answer

Option 4

NTA final key.

Chapter: Vector Algebra
Topic: Cross Product
Idea tested: Lagrange's Identity

Same idea in other shifts

Asked 8× 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 108 of the 174 JEE Main shifts held from 2017 to 2026.