How to Find an Angle With Known Angles

Triangles offer the most common example of how to calculate the degrees of an unkown angle, because the angles always add up to 180 degrees.They often have equal sides, angles or a combination of both, which assist in determining unknown angles. You can find the angle knowing only the length of the sides, or knowing only one or more other angles. Right-angle, isoceles and equilateral triangles all have specific configurations that permit you to simply calculate angles.

Instructions

1. Add the degrees for two known angles in any triangle together. Subtract that sum from 180 to get the degrees for the third angle.

2. With an isoceles triangle, determine which two of the three angles are equal. Add those degrees together and subtract from 180 to get the third angle. If only the third angle is known, subtract its degrees from 180 and divide by 2.

3. With an equilateral triangle, each angle is equal to 60 degrees.

Tips & Warnings

• Mathematical formulas allow you to calculate the angles of oblique triangles, which have no right angles or equal-length sides.

• Geometric and trigonometric functions allow you to calculate angles on other figures than triangles.

References

• University of Colorado at Boulder: Basic Geometry: Triangles, Circles and More
• Clark University: Oblique Triangles; David E. Joyce; 1997