Isosceles & Equilateral Triangles

Front

What is an isosceles triangle?

Back

An isosceles triangle is a triangle that has at least two sides of equal length.

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 to 60°.

Front

If two sides of a triangle are congruent, then the angles opposite those sides are ______________.

Back

congruent.

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 40°, what is the vertex angle?

Back

100°.

Front

If the vertex angle of an isosceles triangle is 80°, what are the measures of the base angles?

Back

50° each.

Front

What is the relationship between the sides and angles in a triangle?

Back

In a triangle, the larger the angle, the longer the opposite side.

Front

How do you find the length of a side in an isosceles triangle given the angles?

Back

Use the properties of triangles and the fact that the sum of angles is 180° to find the unknown angles, then apply the Law of Sines or basic trigonometry.

Front

If the lengths of the two equal sides of an isosceles triangle are 10 cm, what is the minimum length of the base?

Back

The minimum length of the base must be greater than 0 cm but less than 20 cm.

Front

What is the formula for the area of a triangle?

Back

Area = 1/2 * base * height.