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. Also, each interior angle of a triangle is more than zero degrees but less than 180 degrees. Exterior Angle Property. Types of triangles. This is called the exterior angle property of a triangle. ∴ Exterior angle is equal to sum of interior opposite angles Find exterior angle ∠ 1 Here, ∠1 = ∠B + ∠C ( Exterior angle property) ∠1 = 45° + 60° ∠1 = 105° Find exterior angle In ∆ABC, ∠BCD = ∠CAB + ∠ABC (Exterior angle property) ∠BCD = 85° + 25° ∠BCD = 110° Find exterior angle In ∆PQR, Prove that it is equal to the sum of the interior angles on the other two arms. Similarly, this property holds true for exterior angles as well. For more on this see Triangle external angle theorem. Define an exterior angle of a triangle and identify all the exterior angles. Exterior Angle Theorem. Exterior Angle Property - Displaying top 8 worksheets found for this concept.. 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. Example: . Before we begin the discussion, let us have look at what is a triangle. The side opposite to the largest angle of a triangle is the largest side. Properties. Properties. Same goes for exterior angles. Any exterior angle of the triangle is equal to the sum of its interior opposite angles. 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. A polygon is called a plane figure that is bounded by the finite number of line segments for forming a closed figure. 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. Learn the concepts of Class 7 Maths The Triangle and Its Properties with Videos and Stories. One of the basic theorems explaining the properties of a triangle is the exterior angle theorem. This is a fundamental result in absolute geometry because its proof does not depend upon the parallel postulate.. 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 figure is regular all the exterior angles will be equal. Triangles can be classified in 2 major ways: Classification according to internal angles Let us discuss this theorem in detail. Apply this relationship to find unknown angles. 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. Property 2: The sum of an interior angle and its adjacent exterior angle is 180°. 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