Which of the following is not a property of triangles?

The choice stating that the sum of the angles is 150° is not a property of triangles. In a triangle, the sum of the interior angles is always 180°, regardless of the type of triangle. This fundamental property applies universally, meaning it accurately characterizes all triangles.

In contrast, the other options reflect true properties of triangles. A triangle can indeed have at most one right angle, as having more than one would exceed the total of 180° for the sum of the angles. The triangle inequality theorem states that the longest side of a triangle is opposite the largest angle, reinforcing the relationship between side lengths and angles. Lastly, the requirement that any two sides of a triangle must sum to more than the length of the third side is another essential characteristic that ensures that the figure forms a closed shape without any contradictions in measurement.