Invariants Under Transformation Math Example 2

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Example 2

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A rectangle with vertices (0,0)(0,0), (6,0)(6,0), (6,4)(6,4), (0,4)(0,4) is dilated by a scale factor of 22 centered at the origin. Which properties are invariant and which change?

Solution

  1. 1
    Apply dilation: multiply each coordinate by 22. New vertices: (0,0)(0,0), (12,0)(12,0), (12,8)(12,8), (0,8)(0,8).
  2. 2
    Original side lengths: 66 and 44. New side lengths: 1212 and 88. Side lengths are NOT invariant — they doubled.
  3. 3
    Original angles: all 90°90°. New angles: all 90°90°. Angles ARE invariant under dilation.
  4. 4
    Original area: 2424. New area: 96=24Ɨ4=24Ɨ2296 = 24 \times 4 = 24 \times 2^2. Area scales by k2k^2 so it is NOT invariant.
  5. 5
    The ratio of sides: 6:4=3:26:4 = 3:2 and 12:8=3:212:8 = 3:2. Ratios of corresponding lengths ARE invariant.

Answer

AnglesĀ andĀ ratiosĀ ofĀ lengthsĀ areĀ invariant;Ā lengthsĀ andĀ areaĀ change.\text{Angles and ratios of lengths are invariant; lengths and area change.}
Dilation is a similarity transformation. It preserves angle measures and the ratios of corresponding lengths, but changes actual distances by the scale factor kk and areas by k2k^2. The shape is preserved but not the size.

About Invariants Under Transformation

A property of a function is invariant under a transformation if it remains unchanged after the transformation is applied to the function.

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