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You have a non-square matrix A = [1 2 3; 4 5 6] and vector b = [7; 8]. What does x = A\b compute in MATLAB?

hard📝 Application Q15 of 15
MATLAB - Linear Algebra
You have a non-square matrix A = [1 2 3; 4 5 6] and vector b = [7; 8]. What does x = A\b compute in MATLAB?
AThe inverse of A times b
BAn error because A is not square
CA least-squares solution minimizing ||Ax - b||
DA random vector x
Step-by-Step Solution
Solution:
  1. Step 1: Recognize matrix shape and operation

    A is 2x3 (more columns than rows), so system is underdetermined.
  2. Step 2: Understand MATLAB's backslash behavior for non-square A

    MATLAB computes the least-squares solution x that minimizes ||Ax - b|| (minimum norm among solutions).
  3. Final Answer:

    A least-squares solution minimizing ||Ax - b|| -> Option C
  4. Quick Check:

    Backslash solves least-squares for non-square A [OK]
Quick Trick: Backslash gives least-squares solution if A not square [OK]
Common Mistakes:
  • Expecting error for non-square A
  • Thinking it calculates inverse always
  • Assuming exact solution always exists

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