Please help me write a geometry proof about an isosceles triange!?
Prove: If an isosceles triangle has an altitude from the vertex to the base, then the altitude bisects the vertex angle.
Given: Triangle ABC is isosceles; Segment CD is the altitude to base segment AB.
To Prove: Segment CD bisects Angle ACB
Then there are two columns for the proof. One says statements and the other says reasons. There is a picture of the triangle where the base is AB with D in the middle between them. Then the altitude is from D to C and C is on the top. PLEASE help me!