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Matrix Multiplication — 2×2 and 2×1 Cases

To multiply A (m×n) by B (n×p): the (i,j) entry of AB = row i of A dotted with column j of B. Matrix multiplication is NOT commutative.

PrecalculusCommon Core HSN-VM.C.8N-VMVerified correct ✓

Worked examples

Multiply A = [[1, 2], [-4, 0]] by x = [4, 0]ᵀ. What is the second (bottom) entry of Ax?
Answer: -16
Multiply A = [[0, 2], [2, 1]] by x = [2, 1]ᵀ. What is the second (bottom) entry of Ax?
Answer: 5

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