Question

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.

Explanation:

An isosceles triangle is defined as having at least two congruent sides. The base angles (opposite the congruent sides) are congruent. The sides opposite the base angles are the congruent sides. The vertex angle bisector splits the base into two equal parts at a right angle. "All three angles/sides congruent" describes equilateral triangles, a subset of isosceles but not all isosceles triangles.

Answer:

The base angles are congruent., The two sides opposite the base angles are congruent., The bisector of the vertex angle is the perpendicular bisector of the base.