How to Find Missing Angle in a Triangle
Finding a Missing Angle in a Triangle
If any of the angles (A, B or C) is unknown, it can be found as long as the other two angles are known.
How to Find the Missing Angle in a Triangle
Finding the missing angle in a triangle is easy.
What is the missing angle A in the triangle below?
The angles add up to 180°.
A + 65° + 75° = 180°
Find A by subtracting the known angles from 180°.
A = 180° − 65° − 75° = 40°
The missing angle A is 40°.
The slider below shows another real example of how to find the missing angle in a triangle.Open the slider in a new tab
How to Find the Missing Angle in an Equilateral Triangle
In the example above, we found the missing angle in a scalene triangle: a triangle where all three angles are different.
It is even easier to find the missing angle in an equilateral triangle: where all three angles are equal to each other and all three sides are the same length.
All three angles in an equilateral triangle are 60°.
How to Find the Missing Angle in an Isosceles Triangle
An isosceles triangle has two angles that are equal to each other.