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Angle Bisector Theorem Calculator

Online angle bisector calculator. Enter an angle to find the two equal angles created by its bisector, with the property explained—great for geometry basics.

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The bisector makes two equal angles, each half the original
Angle to bisect, 0-180

📖 Tutorial | Angle Bisector

1. Definition
The angle bisector is the ray from the vertex that splits the angle into two equal parts.
2. Formula & Notation
aThe known angle
a/2Each resulting angle
3. Properties & Laws
  • Points on it are equidistant from the sides;
  • Equidistant points lie on it;
  • Three meet at the incenter;
  • Each angle is half the original.
4. Steps
  1. Enter the angle a (0<a<180);
  2. Click "Calculate";
  3. Or click "Load Example".
5. Worked Examples
Example: angle 80°.
Solution: each = 80/2 = 40°.
6. Common Pitfalls
Each angle is half;
It is a ray;
Not a perpendicular bisector.

❓ FAQ | Angle Bisector

What is an angle bisector?
The ray that halves the angle.
How large is each?
Half the original.
Its property?
Points on it are equidistant from the sides.
80° bisected?
Two 40° angles.
Three bisectors of a triangle?
Meet at the incenter.
Line or ray?
A ray from the vertex.