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Angle Bisector Theorem

Rule

Angle Bisector Theorem

An angle bisector of a triangle divides the opposite side into two segments that are proportional to the other two sides of the triangle.

In triangle $A B C,$ bisected by $ℓ,$ the ratio of $A D$ to $A B$ is equal to the ratio of $C D$ to $C B .$ $\frac{A D}{A B} = \frac{C D}{C B}$