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JEE Main 2021 · MathsMultiple choiceSingle correctMediumApplication

JEE Main 26 February 2021, Shift 1, Maths Q73

Question 73 of 90 in this shift, Maths question 13 of 30, Section A.

Let A be a symmetric matrix of order 2 with integer entries. If the sum of the diagonal elements of

A^2

is 1, then the possible number of such matrices is :

(1) $1$
(2) $4$ Official answer
(3) $6$
(4) $12$

Official answer

Option 2

NTA final key.

Chapter: Matrices
Topic: Matrix Multiplication
Idea tested: Trace of A times A Transpose

Same idea in other shifts

Asked 2× in all

8 Jan 2020, Shift 1 · Q72The number of all $3\times3$ matrices A, with enteries from the set $\{-1,0,1\}$ such that the sum of the diagonal elements of $AA^T$ is…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.