Which properties belong to all isosceles triangles? Check all that apply. The base angles are congruent.
All three angles are congruent.
The two sides opposite the base angles are congruent.
All three sides are congruent.
The bisector of the vertex angle is the perpendicular bisector of the base.

3 Answers:  Choice A, Choice C, Choice E

Explanation:

Let's go through the answer choices to see which are true and which are false.

A) True. The base angles are the same measure, and they are opposite the congruent sides. Any isosceles triangle has exactly two congruent sides.B) False. This is describing an equilateral triangle (where all three angles are 60 degrees each).C) True. See choice A.D) False. This is describing an equilateral triangle where all sides are the same length. E) True. You can use the SAS (side angle side) congruence theorem to prove that the angle bisector is also the perpendicular bisector. Furthermore, this segment is also a median. This only applies to the vertex angle.