What type of triangle would contain one angle that is less than 90 degrees?

An acute triangle is defined as a triangle in which all three of its angles are less than 90 degrees. Therefore, if one angle is specifically stated to be less than 90 degrees, it implies that the triangle could potentially be categorized as acute, especially if the other two angles are also less than 90 degrees. In an acute triangle, this property ensures that none of the angles reach or exceed a right angle.

In contrast, an obtuse triangle contains one angle greater than 90 degrees. A right triangle has one angle exactly equal to 90 degrees. While a scalene triangle refers to the lengths of its sides being all different, it does not provide information about the size of the angles. Thus, while scalene triangles can certainly be acute or obtuse, the classification does not guarantee that any angle is specifically less than 90 degrees—only the lengths of the sides differentiate it.

Focusing on the given definition of an acute triangle helps clarify why this option is the best answer when considering a triangle that must include at least one angle measuring less than 90 degrees.