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Class 12 Matrices · Short Answer2 Marksmatrix_multiplication

Class 12 Maths · Matrices · Short Answer #55

For A=\(\begin{bmatrix}1 & -2 & 3\\-4 & 2 & 5\end{bmatrix}\) and B=\(\begin{bmatrix}2 & 3\\4 & 5\\2 & 1\end{bmatrix}\), let BA=[bᵢⱼ]. Find b₂₁+b₃₂.

✅ Step-by-Step Solution

Final Answer: −18
  1. BA is 3×3. Use row 2 of B and column 1 of A to get b₂₁=4·1+5·(−4)=−16.
  2. Use row 3 of B and column 2 of A to get b₃₂=2·(−2)+1·2=−2.
  3. Hence b₂₁+b₃₂=−16−2=−18.

📋 CBSE Stepwise Marking Scheme

  • [0.5 marks] BA is 3×3. Use row 2 of B and column 1 of A to get b₂₁=4·1+5·(−4)=−16.
  • [1 mark] Use row 3 of B and column 2 of A to get b₃₂=2·(−2)+1·2=−2.
  • [0.5 marks] Hence b₂₁+b₃₂=−16−2=−18.

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