Isosceles Triangle

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An isosceles triangle is a triangle having (at least) two sides of equal length, and therefore also with (at least) two equal angles.

Isosceles triangle is an elementary-school-level concept. It is listed in the California State Standards for Grade 3.


Equilateral Triangle: A triangle in which all three sides are of equal length. In such a triangle, the angles are all equal as well.


Angle: An angle is a measure of the amount of rotation about the point of intersection of two lines or line segments that is required to bring one into correspondence with the other.
Triangle: A triangle is a three-sided (and three-angled) polygon.

Classroom Articles on Polygons

  • Decagon
  • Pentagon
  • Dodecagon
  • Polygon
  • Hendecagon
  • Quadrilateral
  • Heptagon
  • Rectangle
  • Hexagon
  • Regular Polygon
  • Nonagon
  • Right Triangle
  • Octagon
  • Square
  • Parallelogram
  • Trapezoid

  • Classroom Articles on Geometry (Up to Elementary-School Level)

  • Acute Angle
  • Perimeter
  • Area
  • Perpendicular
  • Circle
  • Point
  • Cone
  • Prism
  • Cube
  • Pyramid
  • Cylinder
  • Radius
  • Diameter
  • Sphere
  • Geometric Construction
  • Surface Area
  • Obtuse Angle
  • Volume
  • Parallel