Triangle Theorems

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

If two angles of a triangle are 70° each, what is the measure of the third angle?

Back

The third angle is 40°.

Front

What is the value of x in the triangle if one angle is 90° and another is 50°?

Back

x = 40°.

Front

In a right triangle, if one angle is 90°, what is the relationship between the other two angles?

Back

The other two angles must add up to 90°.

Front

What is the definition of an isosceles triangle?

Back

An isosceles triangle is a triangle with at least two equal sides and two equal angles.

Front

What is the definition of an equilateral triangle?

Back

An equilateral triangle is a triangle where all three sides and all three angles are equal, each measuring 60°.

Front

If one angle of a triangle is 135°, what can you say about the other two angles?

Back

The other two angles must be acute and their sum must be 45°.

Front

What is the exterior angle theorem?

Back

The exterior angle of a triangle is equal to the sum of the two opposite interior angles.

Front

If a triangle has angles measuring 30° and 60°, what is the measure of the third angle?

Back

The third angle measures 90°.

Front

What is the relationship between the angles in a triangle and a straight line?

Back

The angles in a triangle and a straight line must add up to 180°.