How do you find the measure of a missing angle in a triangle? A triangle has three sides and three interior angles. No matter which type of triangle you are dealing with, such as equilateral, scalene, right-angle triangle, or isosceles, the sum of all interior angles is equal to 180˚. So, what if there is a missing angle in an equilateral triangle, well, each angle in this shape is equal to 60° . Therefore, the missing angle will be 60°. In a right triangle, one angle is 90° , here you can simply add 90° and the angle provided and subtract the sum from 180° . In the case of isosceles, two sides are equal, which means two angles are equal. You can subtract the angle opposite to the unequal side from 180° and then divide the answer by two, and you will get the missing angle. If the angle of the unequal side is to be found, you simply multiply the provided angle by two and subtract the answer from 180° .

We start off with the super obvious premise that the sum of all angles within a triangle is equal to 180 degrees. That can springboard us to understand any missing angles I your everyday typical triangle. Over the course of most worksheets and lessons you will given the value of at least two angles to find the third and final angle just take the sum of those angles and find the difference of them from 360 degrees. We encourage all students to get in the habit of checking all their answers (just remember that all measurements within a triangle must add up to 180 degrees).