Question

One angle in an obtuse isosceles triangle measures 40°. What are the measures of the other two angles?

40° and 120°
70° and 70°
40° and 100°
80° and 80°

Answer 1

40° and 100°

Explanation:

An obtuse triangle has one obtuse angle, or an angle that measures more than 90° but less than 180°. Options 1 and 2 are not correct, because these are acute angles.

So, one of the angles must be 40°, and the other may be 100° or 120°.

The measures of the angles in a triangle add up to 180°

40° + 40° +
`x` = 180°

80° +
`x` = 180°

`x` = 180° - 80°

`x` = 100°

The other two angles are 40° and 100°.

Answer 2

The answer would be 70 and 70 because an isosceles triangle has 2 equal angles and one irregular angle that all add up to 180 degrees