Answer:
See below.
Explanation:
By definition the median of the triangle bisects the base of the isosceles triangle.
We need to prove that the 2 triangles formed by the median are congruent.
If the 2 triangles are ABD and ACD where BD is the median and < ABC is the angle from which BD is drawn.
BD = BD ( the common side)
AD = DC ( because BD is the median).
AB = AC ( because ABC is an isosceles triangle).
So Triangles ABD and ACD are congruent by SSS.
Therefore m < ABD = m < CBD, so BD is the bisector of < ABC.
To prove BD is also the altitude:
Triangles ABD and CBD are congruent as we have just proven. Therefore the
of measure of the base angle ABD = m < CBD . Also they are adjacent angles ( on the same line) so they add up to 180.
Therefore angles ABD and CBD are both right angles and BD is the altitude of triangle ABC.