Answer:
40
Step-by-step explanation:
Angles of a triangle add up to 180°. An isosceles triangle has two equal sides and two equal angles.
If the 100° angle is one of these base angles, then the other base angle would also be 100°, and their sum would be greater than 180°, so this is not possible.
Therefore, the 100° angle must be the vertex angle. So the base angles are:
100 + 2x = 180
2x = 80
x = 40
