What Are Bisectors?

Bisectors cut things in half

Bisectors are lines (or segments, or rays) that cross directly through the midpoint (middle) of a line segment or the middle of an angle.

• When cutting a line segment in half, the bisector is called a segment bisector.
• When cutting an angle in half, the bisector is called an angle bisector.

In the image above, the blue lines (the line passing through B and ray ZH) bisect the angle and line segment they pass through. The red segment (WX) does not bisect the line it passes through (DE).

When a bisector passes through the midpoint of a line segment, the segments created on either side will both have a length that's equal to exactly half the length of the original segment (which is what happens with line FG, above). Bisectors can intersect with the lines they cut through from any angle.

When a bisector passes through the middle of an angle, the new angles that have the bisector as one of their sides will always have equal measure. That measure will always be half of the original angle's measure.