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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 value of
\((A-2 I)^2-(2 A+I)^2+11 A\) is :

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

Answer & Solution

Correct Answer

(C) \(3I\)

Step-by-step Solution

Detailed explanation

\((A-2 I)^2 = A^2 - 4AI + 4I^2 = A - 4A + 4I = -3A + 4I\) \((2 A+I)^2 = 4A^2 + 4AI + I^2 = 4A + 4A + I = 8A + I\) \((A-2 I)^2-(2 A+I)^2+11 A = (-3A + 4I) - (8A + I) + 11A\) \(= -3A + 4I - 8A - I + 11A\) \(= (-3 - 8 + 11)A + (4 - 1)I\) \(= 0A + 3I = 3I\)
From CUET
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