2.2 Triangles

  • Types Properties of Triangles • Perimeter Area • Hero’s Formula • Pythagorean Theorem • Similar Triangles

When part of a plane is bounded closed by straight-line segments, it is called a polygon, it is named according to the number of sides it has. A triangle has three sides, a quadrilateral has four sides, a pentagon has five sides, a hexagon has six sides, so on. The most important polygons are the triangle, which we consider in this section, the quadrilateral, which we study in the next section.


In a scalene triangle, no two sides are equal in length. In an isosceles triangle, two of the ...

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