Matrix Dilations

You've seen this before! Drag the vectors around to create the following transformations:
A Dilation.
A Dilation with a scale factor of -2.
A Dilation composed with a Rotation.
A Dilation composed with a Reflection.
A Dilation with a scale factor of 3.
A Dilation with a scale factor of sqrt(5).
A Dilation with a scale factor of sqrt(13).

What must be true of the vectors that make up the matrix that produces a dilation?

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Steve Phelps, Created with GeoGebra