How to Find Missing Angle Measures in an Isosceles Triangle: Step-by-Step Guide

Learn how to calculate missing angles in an isosceles triangle using simple subtraction and division. Easy steps explained clearly.

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To find the missing angle measures of an isosceles triangle, first identify the two equal angles, which are opposite the equal sides. If one equal angle is known, subtract its measure from 180° and then divide by 2 to find the remaining angles. For example, if one angle is 40°, subtract 40° from 180° to get 140°, then divide 140° by 2 to get 70°. Each of the missing angles is 70°.

FAQs & Answers

  1. What is an isosceles triangle? An isosceles triangle is a triangle with at least two equal sides and two equal angles opposite those sides.
  2. How do you calculate the missing angles in an isosceles triangle? To find missing angles, subtract the known angle from 180° and divide the result by 2 to find the measure of each unknown equal angle.
  3. Why do the two base angles in an isosceles triangle have the same measure? Because the sides opposite those angles are equal in length, the corresponding base angles are congruent.

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