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How does a 2x2 matrix transform the unit square into a parallelogram?

A 2x2 matrix transforms the unit square by mapping its standard basis vectors to the matrix's columns. The first column represents the image of the first basis vector, and the second column represents the image of the second basis vector. These two transformed vectors form the adjacent sides of a parallelogram, which is the transformed unit square.

Conditions

  • The matrix is 2x2.
  • The transformation is linear.
  • The unit square is defined by the standard basis vectors e1=(1,0)e_1=(1,0) and e2=(0,1)e_2=(0,1).

Reasoning, step by step

  1. Identify the columns of the 2x2 matrix.
  2. Recognize that multiplying the matrix by e1e_1 selects the first column.
  3. Recognize that multiplying the matrix by e2e_2 selects the second column.
  4. Visualize the unit square's edges transforming into these two column vectors.
  5. Observe that the resulting shape is a parallelogram spanned by these columns.

Example

The script states: 'Multiplying a matrix by the first or second standard basis vector selects its corresponding column. These two images determine the transformed unit square.'

Common misconceptions

  • Believing that the rows of the matrix determine the transformed shape directly (for column vectors, it is the columns).
  • Thinking that the unit square remains a square after transformation.
  • Confusing the determinant value with the side lengths of the parallelogram.

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