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 also 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

The vertex angle is 100°.

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

How do you find the length of each side of an equilateral triangle if the perimeter is known?

Back

Divide the perimeter by 3 to find the length of each side.

Front

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

Back

Each side is 7 meters.

Front

What is the relationship between the angles in an isosceles triangle?

Back

The angles opposite the equal sides are equal.

Front

How do you calculate the vertex angle of an isosceles triangle?

Back

Subtract the sum of the base angles from 180°.

Front

If the base angles of an isosceles triangle are both 45°, what is the vertex angle?

Back

The vertex angle is 90°.

Front

What is the formula for the area of a triangle?

Back

Area = 1/2 * base * height.