Answer:
20°
Step-by-step explanation:
An Isosceles triangle is a triangle having two sides with the same length. The general form of this type of triangles is shown in the figure marked as 1 below. As you can see, two sides are equals and they are represented by the harsh marks. Since two sides are equals, then there will be two equal angles as well. If one angle measures 140°, then there is only one possibility:
1. The given angle is opposite to the side where the two equal angles lies:
This is the case of the figure marked as 2. Since the internal angles of a triangle add up to 180°, then it is true that:
2x + 140° = 180° ∴ 2x = 40° ∴ x = 20°
It's impossible that the given angle lies on one of the two equal angles as indicated in figure marked as 3, because in this case we'd have two angles that measure 140° each, but 140° + 140° is greater than 180°, so this is impossible for internal angles of a triangle.
