The Definiton of a Triangle
Examples of triangles Properties of triangles Classification of triangles Non-euclidean triangles Examples of Triangles A triangle is a special kind of shape. What do you think makes a shape a triangle?
Be sure to think about this question before going on with the lesson
Properties of triangles A figure is closed if all its sides are connected.
These figures are closed. These figures are not closed. Mathematicians define a triangle to be a closed figure with three sides.
Use this definiton to figure out which of the following shapes are triangles.
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Can you think of any triangles that you see in your everyday life?
(Hint: look at bridges or radio towers.)
Classification of Triangles There are many different kinds of triangles.
Acute trianlges are triangles in which the measures of all three angles are less than 90 degrees. Obtuse triangles are triangles in which the measure of one angle is greater than 90 degrees. Right triangles are triangles in which the measure of one angle equals 90 degrees. Equilateral triangles are triangles in which all three sides are the same length. Isosceles triangles are triangles in which two of the sides are the same length. Scalene triangles are triangles in which none of the sides are the same length.
