Isosceles and Equilateral Triangles

Front

What is an isosceles triangle?

Back

An isosceles triangle is a triangle that has at least two sides of equal length and the angles opposite those sides are equal.

Front

What is an equilateral triangle?

Back

An equilateral triangle is a triangle in which all three sides are of equal length and all three angles are equal, each measuring 60°.

Front

If an isosceles triangle has a base angle of 40°, what is the vertex angle?

Back

100°

Front

What is the formula for the perimeter of a triangle?

Back

The perimeter of a triangle is the sum of the lengths of its sides.

Front

If the perimeter of an equilateral triangle is 21 meters, what is the length of each side?

Back

7 meters

Front

What is the sum of the interior angles of a triangle?

Back

The sum of the interior angles of a triangle is always 180°.

Front

In an isosceles triangle, if the base angles are equal, what can be said about the sides opposite those angles?

Back

The sides opposite the equal angles are also equal in length.

Front

How do you find the measure of an angle in an isosceles triangle if you know the base angles?

Back

Subtract the sum of the base angles from 180° to find the vertex angle.

Front

What is the relationship between the sides and angles in an equilateral triangle?

Back

In an equilateral triangle, all sides are equal, and all angles are equal to 60°.

Front

If one angle of a triangle measures 135°, what can be said about the other two angles?

Back

The other two angles must sum to 45° since the total must equal 180°.