How to Figure Angles of a Triangle

An isosceles triangle has two angles that are identical in width.

The sum of all the angles of any triangle always equals 180 degrees. No matter what a triangle looks like or how different the length of each side is, the angles always add up to the same number. In a right triangle, a triangle that has one right angle and two acute angles, it becomes even simpler to find the width of the remaining angles because you already know the width of one of the angles. If you follow simple rules and remember that all the angles always add up to one number, then the solution to the size of the other angles is never far away.

Things You'll Need

• Protractor

Instructions

1. Use a protractor to measure one of the acute angles in a right triangle. Add the width of the angle to 90 (the measurement in degrees of a right angle) and subtract the sum from 180 (the total sum in degrees of all angles in a triangle). The number you have calculated is the width of the remaining angle.

2. Measure the unequal angle in an isosceles triangle. The remaining two angles in an isosceles triangle are always equal. Subtract the number from 180 degrees and divide the number by two. The number you have deduced is the width of each of the equal angles.

3. Remember that in an equilateral triangle, there is no need to calculate the angles. Each angle is always 60 degrees in an equilateral triangle.

Tips & Warnings

• Use a calculator if you having trouble with the math involved. Always use a protractor to measure angles rather than trying to guess at their measurements.

References

• The Geometry Center: Triangles