Question

Select all that apply.

In an isosceles triangle, one angle measures 20°. What are the measures of the other two angles?
80° and 80°
90° and 90°
20° and 140°
20° and 60°

Answer 1

All of a triangles angles add up to 180, this is known as the triangle sum conjecture.


an Iscoceles triangle is a triangle that has two or more congruent sides.

if a triangle is Iscoceles then th e two angles that are made by the congruent sides and base are also congruent.

if you know that one of the angles is 20 that. The sum of the other two angles must be 160.

That means that answer 2 and 4 are incorrect.

Answers 1 and 3 both have a total angle sum of 160. since this is true the correct answer depends on where the known angle is. If it is the angle that is formed by the two congruent sides than the answer is number one. but if it is formed by one of the congruent sides and the base then the answer is number 3.

Answer 2

Answer: 80° and 80°

20° and 140°

Explanation:

An isosceles triangle is a kind of triangle that has two equal angles.

Given : In an isosceles triangle, one angle measures 20°.

If it is one of the equal angles , then one other angle must measures 20°.

and Third angle = 180°- 20°- 20° [ By Angle sum property of triangle]

= 140°

i.e. the measures of other two angles would be 20° and 140°.

If it is not one of the equal angle then we let the measure of equal angles as x.

By angle sum property of triangle , we have

x+x+20°=180°

⇒ 2x = 160°

⇒ x =80°

i.e. measures of other two angles would be 80° and 80°.

Thus , the correct choices are :

80° and 80°

20° and 140°