The measure of the missing angle indicated by ? is equal to 125°
The exterior angles of a triangle are the angles formed outside the triangle, but adjacent to its sides.When a triangle is formed by two intersecting lines, each of the lines extended beyond the point of intersection forms two exterior angles. Also an exterior angle of a triangle is equal to the sum of the two opposite interior angles.
Considering the triangle with an angle 25°, it has another interior angle 55° which make the third angle to be:
180 - (25 + 55) = 100°
Considering the exterior angle 155°, 100° will be one of its opposite interior angles, let the other that share same line with the missing angle be x so that we solve for x as follows:
x + 100° = 155
x = 155° - 100°
x = 55°
missing angle ? = 180 - 55 {sum of angles on a straight line}
? = 125°
Therefore, we have the measure of the angle indicated as ? to be 125°.
Complete question:
Find the missing angle ?.