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CUET · MATHS · PYQ PAPER 2025

If \(A\) is a square matrix such that \(A^2=A\) and \(I\) is the identity matrix of same order as \(A\), then the matrix \((2 I+A)^3-19 A-3 I\) is equal to

  1. A \(5 I\)
  2. B \(5 A\)
  3. C \(7 I\)
  4. D \(7 A\)
Verified Solution

Answer & Solution

Correct Answer

(A) \(5 I\)

Step-by-step Solution

Detailed explanation

\((2 I+A)^2 = 4 I^2+4 IA+A^2 = 4I+4A+A = 4I+5A\) \((2 I+A)^3 = (2 I+A)(4 I+5 A) = 8 I^2+10 IA+4 AI+5 A^2 = 8 I+10 A+4 A+5 A = 8 I+19 A\) \((2 I+A)^3-19 A-3 I = (8 I+19 A)-19 A-3 I = 5 I\)