91Ó°ÊÓ

Set up and prove: The altitude to the base of an isosceles triangle divides the triangle into two congruent triangles.

Prove: An altitude of an equilateral triangle is also a median of the triangle.

Prove: Corresponding medians of congruent triangles are congruent.

Prove: The median to the base of an isosceles triangle bisects the vertex angle.

Draw an obtuse triangle PQR with longest side PR. Then draw equilateral triangles APQ and BQR lying outside the given triangle. Assuming that the measure of each angle of an equilateral triangle is \(60,\) prove that \(\overline{\mathrm{AR}} \cong \overline{\mathrm{PB}}\)

How many different isosceles triangles can you find that have sides that are whole-number lengths and that have a perimeter of \(18 ?\)