Choose the measure before the multiplier
Geometrically similar figures have the same shape. If every corresponding length is multiplied by a positive factor \(k\), every corresponding area is multiplied by \(k^2\), and every volume by \(k^3\). Perimeters follow the length factor.
The rectangles above have length factor 2, but their areas are \(2\text{ cm}^2\) and \(8\text{ cm}^2\): an area factor of 4. Doubling three perpendicular dimensions gives a volume factor of 8.
| Measure | Ratio, small : large |
|---|---|
| Corresponding length or perimeter | \(a:b\) |
| Area or corresponding surface area | \(a^2:b^2\) |
| Volume or capacity | \(a^3:b^3\) |
Write the direction of your ratio before substituting. Similar heights alone do not prove two arbitrary solids geometrically similar; all corresponding dimensions must have the same factor.
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