One angle of an isosceles triangle measures 140°. Which other angles could be in that isosceles triangle? Choose all that apply.

Question

Is my answers are-(75) (30) (35) (20)

Answer 1

There is only one possibility. 1. The obtuse angle is 140 leaving the two acute angles to measure 20 degrees each. 2. The other possibility is not possible. There cannot be two obtuse angles in a triangle due to the fact that the triangle sum equals 180.

Answer 2

There are two key ideas here that will lead you to the answer.

1) The interior angles of all triangles add up to 180 degrees.

2) By definition, an isosceles triangle has two sides that are the same length and thus two angles that are equal.

If one of your angles is 140 degrees, that leaves 180-140 = 40 degrees left for the remaining two angles, which again have to be the same. So now you just have to split 40 evenly between the two angles, and there is one answer choice available that suffices.