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 the vertex angle in an isosceles triangle?

Back

The vertex angle in an isosceles triangle is the angle formed by the two equal sides.

Front

If one base angle of an isosceles triangle measures 40°, what is the measure of the vertex angle?

Back

The vertex angle measures 100°.

Front

In triangle DEF, if DE = x + 7, DF = 3x – 1, and EF = 2x + 5, how do you find the value of x?

Back

Set the two equal sides (DE and DF) equal to each other and solve for x.

Front

What is the sum of the angles in any triangle?

Back

The sum of the angles in any triangle is always 180°.

Front

What are the properties of an equilateral triangle?

Back

An equilateral triangle has all three sides of equal length and all three angles measuring 60°.

Front

How do you calculate the measure of the vertex angle if the base angles are known?

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 isosceles triangle?

Back

In an isosceles triangle, the angles opposite the equal sides are equal.

Front

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

Back

The vertex angle measures 90°.

Front

How can you determine if a triangle is isosceles based on its side lengths?

Back

If two sides of a triangle are of equal length, then the triangle is isosceles.