In this article, we will learn about: Triangle exterior angle theorem, exterior angles of a triangle, and, how to find the unknown exterior angle of a triangle. This is called the exterior angle property of a triangle. For more on this see Triangle external angle theorem. If the figure is regular all the exterior angles will be equal. Property 3: Exterior Angle Theorem An exterior angle of a triangle is equal to the sum of the two opposite interior angles. The side opposite to the largest angle of a triangle is the largest side. Exterior Angle Theorem. Let us discuss this theorem in detail. In any geometrical figure, whether regular or irregular, and with any number of sides, the sum of the exterior angles will always be 360 degrees. Exterior Angle Property. Prove that it is equal to the sum of the interior angles on the other two arms. The exterior angle theorem is Proposition 1.16 in Euclid's Elements, which states that the measure of an exterior angle of a triangle is greater than either of the measures of the remote interior angles. If the equivalent angle is taken at each vertex, the exterior angles always add to 360° In fact, this is true for any convex polygon, not just triangles. Properties. This is a fundamental result in absolute geometry because its proof does not depend upon the parallel postulate.. Properties. Types of triangles. Same goes for exterior angles. For a triangle: The exterior angle d equals the angles a plus b.; The exterior angle d is greater than angle a, or angle b. Before we begin the discussion, let us have look at what is a triangle. One of the basic theorems explaining the properties of a triangle is the exterior angle theorem. An exterior angle of a triangle is equal to the sum of the opposite interior angles. Learn the concepts of Class 7 Maths The Triangle and Its Properties with Videos and Stories. Exterior Angle Theorem. Apply this relationship to find unknown angles. Example: . For more on this see Triangle external angle theorem. Any exterior angle of the triangle is equal to the sum of its interior opposite angles. Similarly, this property holds true for exterior angles as well. Define an exterior angle of a triangle and identify all the exterior angles. Triangles can be classified in 2 major ways: Classification according to internal angles ; If the equivalent angle is taken at each vertex, the exterior angles always add to 360° In fact, this is true for any convex polygon, not just triangles. A polygon is called a plane figure that is bounded by the finite number of line segments for forming a closed figure. An exterior angle of a triangle is equal to the sum of the opposite interior angles. The exterior angle theorem is amongst the most basic theorems of triangles in geometry. 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