Difference between revisions of "Similarity (geometry)"
m |
Made in 2016 (talk | contribs) m |
||
| Line 3: | Line 3: | ||
More formally, we say two objects are [[congruent (geometry)|congruent]] if they are the same up to translation, rotation and reflection ([[rigid motion]]s). We say two objects are similar if they are congruent up to a [[dilation]]. | More formally, we say two objects are [[congruent (geometry)|congruent]] if they are the same up to translation, rotation and reflection ([[rigid motion]]s). We say two objects are similar if they are congruent up to a [[dilation]]. | ||
| − | All circles are similar. Two [[triangle]]s are similar if they have the same [[angle]]s ( | + | All circles are similar. Two [[triangle]]s are similar if they have the same [[angle]]s ([[AA similarity]]), and since the sum of the angles of any triangle is 180 [[degree (geometry) | degrees]], this means that two triangles are similar if they have two equal angles (AA similarity). Equivalently, two triangles are similar if their corresponding sides are in equal [[ratio]]s. Two [[polygon]]s are similar if their corresponding angles are equal and corresponding sides are in a fixed ratio. Note that for polygons with 4 or more sides, both of these conditions are necessary. For instance, all [[rectangle]]s have the same angles, but not all rectangles are similar. |
Revision as of 14:41, 18 February 2019
Informally, two objects are similar if they are similar in every aspect except possibly size or orientation. For example, a globe and the surface of the earth are, in theory, similar.
More formally, we say two objects are congruent if they are the same up to translation, rotation and reflection (rigid motions). We say two objects are similar if they are congruent up to a dilation.
All circles are similar. Two triangles are similar if they have the same angles (AA similarity), and since the sum of the angles of any triangle is 180 degrees, this means that two triangles are similar if they have two equal angles (AA similarity). Equivalently, two triangles are similar if their corresponding sides are in equal ratios. Two polygons are similar if their corresponding angles are equal and corresponding sides are in a fixed ratio. Note that for polygons with 4 or more sides, both of these conditions are necessary. For instance, all rectangles have the same angles, but not all rectangles are similar.
This article is a stub. Help us out by expanding it.
