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What is the determinant of the matrix with columns (3,1) and (2,1)?

The determinant is 1. This is calculated using the formula for a 2x2 matrix where the columns are (3211)\begin{pmatrix} 3 & 2 \\ 1 & 1 \end{pmatrix}. The determinant is (3)(1)−(2)(1)=3−2=1(3)(1) - (2)(1) = 3 - 2 = 1. This value corresponds to the area of the parallelogram formed by these vectors.

Conditions

  • The matrix has columns (3,1)(3,1) and (2,1)(2,1).
  • The determinant formula ad−bcad-bc is applied correctly to the column entries.

Reasoning, step by step

  1. Construct the 2x2 matrix with the given columns: (3211)\begin{pmatrix} 3 & 2 \\ 1 & 1 \end{pmatrix}.
  2. Identify a=3,b=2,c=1,d=1a=3, b=2, c=1, d=1 (based on column positions in the standard determinant expansion for columns).
  3. Apply the formula: (3×1)−(2×1)(3 \times 1) - (2 \times 1).
  4. Calculate the result: 3−2=13 - 2 = 1.

Example

The script states: 'The columns (3,1) and (2,1) form a parallelogram of area one. The matrix determinant agrees: 3(1)−2(1)=13(1)-2(1)=1.'

Common misconceptions

  • Swapping the subtraction order (2(1)−3(1)2(1)-3(1)).
  • Treating the inputs as rows instead of columns without adjusting the formula.
  • Calculating the trace instead of the determinant.

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