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A bisector is an object which bisects another object.

Angle Bisector


Let $\angle ABC$ be an angle.

The angle bisector of $\angle ABC$ is the straight line which bisects $\angle ABC$.

In the above diagram, $BD$ is the angle bisector of $\angle ABC$.

Thus $\angle ABD \cong \angle DBC$ and $\angle ABD + \angle DBC = \angle ABC$.

Line Bisector

Definition:Line Bisector

Perpendicular Bisector

Let $AB$ be a line segment.

The perpendicular bisector of $AB$ is the straight line which:

is perpendicular to $AB$
passes through the point which bisects $AB$.


Midpoint of Line

Let $L = AB$ be a line segment whose endpoints are $A$ and $B$.

Let $M$ be a point on $L$ such that the line segment $AM$ is equal to the line segment $MB$.

That is, let $M$ be the bisector of $L$.

Then $M$ is the midpoint of $L$.