Bisecting an angle means cutting it into two equal halves — using only a compass and a straightedge, no protractor needed.
Drag the ray
80°
acute angle
Walk through
Step 1 of 4
1. Arc across both arms
Put the compass point on the vertex. Draw an arc that crosses both arms of the angle — call the crossings A and B.
It works because the vertex, A, B and C make a kite (or rhombus) — and a kite's diagonal bisects the angle it passes through. Drag the angle widget above to any size; the same four steps halve it.
Your turn
You bisect a 116° angle. What's the size of each half?