Geometry Course/Polygon/Triangle

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Triangle[edit | edit source]

Triangle rectangle amb altura - Right-angled triangle with height.svg

A triangle is a two dimensional polygon that has three sides and three angles with the total sum of the angles equal to 180o

Three Points A, B, C
Three sides AB, BC, CA
Three angles , ,
The sum of Three angles

Similar and Congruent Triangles[edit | edit source]

Similar Triangles[edit | edit source]

Congruent Triangles[edit | edit source]

Two Triangles are equal or congruent when

  • Two triangles have three sides are equal . Side by Side by Side (SSS)
  • Two triangles have two sides and angle in between the sides are equal . Side Angle Side(SAS)
  • Two triangles have two angles and the side in between the angles are equal . Angle Side Angle (ASA)

Note that there is no AAA congruence(Angle-Angle-Angle) , because then the sides can be different , making it unequal. It can be similar however.

If you were to transpose one congruent triangle with the other , they would superimpose exactly.

Properties[edit | edit source]

  1. Perimeter
  2. Area

Special Types of Triangle[edit | edit source]

  1. Right Triangle
  2. Isosceles Triangle
  3. Equilateral Triangle
  4. Scalene Triangle