Property 3: Exterior Angle Theorem An exterior angle of a triangle is equal to the sum of the two opposite interior angles. Let us discuss this theorem in detail. 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. ; 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. An exterior angle of a triangle is equal to the sum of the opposite interior angles. This is a fundamental result in absolute geometry because its proof does not depend upon the parallel postulate.. Same goes for exterior angles. Exterior Angle Theorem. Types of triangles. A polygon is called a plane figure that is bounded by the finite number of line segments for forming a closed figure. Example: . 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. Learn the concepts of Class 7 Maths The Triangle and Its Properties with Videos and Stories. Prove that it is equal to the sum of the interior angles on the other two arms. Also, each interior angle of a triangle is more than zero degrees but less than 180 degrees. 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°. 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. 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. Define an exterior angle of a triangle and identify all the exterior angles. If the figure is regular all the exterior angles will be equal. This is called the exterior angle property of a triangle. Before we begin the discussion, let us have look at what is a triangle. For more on this see Triangle external angle theorem. Properties. 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. An exterior angle of a triangle is equal to the sum of the opposite interior angles. For more on this see Triangle external angle theorem. Properties. Exterior Angle Property - Displaying top 8 worksheets found for this concept.. Apply this relationship to find unknown angles. 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