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| | [[Image:Triangle.png|right]] | | [[Image:Triangle.png|right]] |
| − | A '''triangle''' is a three-sided [[geometric]] [[shape]], made by any three points that are not [[collinear]]. | + | A '''triangle''' is a three-sided [[geometric]] [[shape]]. |
| | + | In [[Euclidean geometry]], each side of a triangle is perfectly straight, and the sum of the internal angles of a triangle is always 180º. |
| | + | A triangle is defined by any three points that are not [[collinear]]. |
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| | + | In political ideology, a triangle symbolizes change as the [[Greek]] delta symbol. Usually demands for change are to move towards [[socialism]] and away from the [[U.S. Constitution]] and principles of a [[constitutional republic]]. |
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| | + | ==Naming conventions== |
| | + | Usually, the vertices of a triangle are counter-clockwise denoted by big Latin letters, while small Latin letters are used for the sides: Each side will have the same letter as the opposite vertex. |
| | + | The angles are denoted by Greek letters, if possible, the letter of an angle will correspond to the letter of the adjacent vertex. |
| | + | Often, the sides will be referenced by the adjacent vertices: in the triangle on top of this page, we have <math>a = \overline{BC} = \overline{CB}, b = \overline{CA} = \overline{CA}, c = \overline{BA} = \overline{AB} </math>. |
| | + | Similarly, the angles are denoted as <math>\alpha = \angle CAB, \beta = \angle ABC, \gamma = \angle BCA</math>. |
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| − | In [[Euclidean geometry]], each side of a triangle is perfectly straight, and the sum of the internal angles of a triangle is always 180º.
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| | ==Types of triangles== | | ==Types of triangles== |
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| | An '''obtuse triangle''' has one angle that measures more than 90<sup>o</sup>. | | An '''obtuse triangle''' has one angle that measures more than 90<sup>o</sup>. |
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| − | ==Naming conventions== | + | {| class="wikitable" |
| − | Usually, the vertices of a triangle are counter-clockwise denoted by big Latin letters, while small Latin letters are used for the sites: Every site will have the same letter as the opposite vertex.
| + | |- |
| − | The angles are denoted by Greek letters, if possible, the letter of an angle will correspond to the letter of the adjacent vertex.
| + | |<!--col1-->[[Image:Right-triangle.png|150px]] |
| − | Often, the sides will be referenced by the adjacent vertices: in the triangle on top of this page, we have <math>a = \overline{BC} = \overline{CB}, b = \overline{CA} = \overline{CA}, c = \overline{BA} = \overline{AB} </math>.
| + | |<!--col2-->[[Image:Isoscles-triangle.png|150px]] |
| − | Similarly, the angles are denoted as <math>\alpha = \angle CAB, \beta = \angle ABC, \gamma = \angle BCA</math>.
| + | |<!--col3-->[[Image:Equilateral-triangle.png|150px]] |
| | + | |<!--col4-->[[Image:Obtuse-triangle.png|150px]] |
| | + | |- |
| | + | |<!--col1-->Right Triangle |
| | + | |<!--col2-->Isosceles Triangle |
| | + | |<!--col3-->Equilateral Triangle |
| | + | |<!--col4-->Obtuse Triangle |
| | + | |- |
| | + | |<!--col1--><math>\angle CBA =90^\circ = \pi/2</math> |
| | + | |<!--col2--><math>\angle BCA = \angle CAB </math> |
| | + | |<!--col3--><math>\angle ABC = \angle BCA = \angle CAB</math> |
| | + | |<!--col4--><math>\angle ACB > 90^\circ</math> |
| | + | |}<!--end wikitable--> |
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| | ==Congruence of triangles== | | ==Congruence of triangles== |