Question

One angle measure in an acute isosceles triangle is 20°. What is the measure of one of the other angles?

80°
20°
140°
160°

Answer 1

Answer: FIRST OPTION.

Explanation:

It is important to remember that an Acute Isosceles triangle has two congruent sides and all its angles measure less than 90 degrees. Then, the third option and the the fourth option are not one of the other angles.

You know that the sum of the interior angles of a triangle is 180 degrees.

Then, let be "x" one the other angles, let's check the first option:

`80\°+20\°+x=180\°\\x=80\°`

Since
`80\°<90\°`, the angle provided in the first option is one of the other angles.

Let's check the second option:

`20\°+20\°+x=180\°\\x=140\°`

Since
`140\°>90\°`, the angle provided in the second option is not one of the other angles.

Answer 2

Option 2) 20°

Explanation:

Step 1: Write relevant properties of triangle.

All 3 sides of a triangle are equal to 180 degrees.

In an isosceles triangle, 2 sides and 2 angles are same.

Step 2: Calculate another angles

Since it is an isosceles triangle, two sides will be same therefore, 2 angles will be same.

Angle 1 = Angle 2 = 20 degrees (because isosceles triangle)

Therefore, 20° is the measure of one of the other angles.

Option 2

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