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Definition: A triangle is a polygon with 3 sides.

Types of triangles by sides   Definitions   Directions for interactivity

  • Scalene triangle has three different sides.
  • Isoceles triangle has two equal sides.
  • Equilateral triangle has three equal sides.
("equal" or "congruent" sides, that is, having equal length)
Directions: In the interactivity, click and drag the sliders for side length and notice
  • what kind of triangle is generated.
  • equal sides means equal angles!
Click and drag slider zoom to zoom in or out (and get similar triangles!).
Click and drag point А to move and point В to rotate.
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Rule: The sum of the inside angles? of a triangle is 180°.

Types of triangles by angles   Definitions   Directions for interactivity

  • Acute triangle is a triangle with all three inside angles <90°.
  • Right triangle is a triangle with one inside angle =90°.
  • Obtuse triangle is a triangle with one inside angle >90°.
Directions: In the interactivity, click and drag the angle sliders \alpha and \beta and notice
  • the third angle \gamma is automatically fixed by the formula \alpha + \beta + \gamma = 180^\circ
  • the change in the type of triangle that is created.
Click and drag slider zoom to zoom in or out (and get similar triangles!).
Click and drag point А to move and point В to rotate.
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Formulas for perimeter and area

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Page last modified on March 07, 2008, at 01:42 PM