Exterior Angle Of A Triangle And Its Property

The Exterior Angle of a Triangle

If we extend any side of the triangle then we get an exterior angle.

  • An exterior angle must form a linear pair with one of the interior angles of the triangle.
  • There are only two exterior angles possible at each of the vertices.
Exterior Angle Property of the Triangle

An Exterior angle of a triangle will always be equal to the sum of the two opposite interior angles of the triangle.

Here, ∠d = ∠a + ∠b

This is called the Exterior angle property of a triangle.


Find the value of “x”.


x is the exterior angle of the triangle and the two given angles are the opposite interior angles.


x = 64°+ 45°

x = 109°

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