In triangle , is a median, is a point on , and is the intersection of with .
Prove: If , then is an angle bisector.
In triangle , is a median, is a point on , and is the intersection of with .
Prove: If , then is an angle bisector.
Let be the projections of , and onto the line . The right triangles and are congruent, since is the midpoint of and the acute angles at are equal. This implies that .
In the triangle , is parallel to , and thus
The right triangles and are similar, as the angles at are equal. This implies , which, together with the previous relationship, leads to .
Replacing in the initial relationship with , we get:
, which simplifies to and finally to .
According to the converse of the Angle Bisector Theorem, .
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