Final answer:
An acute-angled triangle has all three angles measuring less than 90 degrees. Other types of triangles vary based on angle measurements and side lengths. Option A is correct.
Step-by-step explanation:
A triangle that has all three angles measuring less than 90 degrees is an acute-angled triangle. The different types of triangles are classified based on their angles and sides.
Apart from acute-angled triangles, there are right-angled triangles with one 90-degree angle, obtuse-angled triangles with one angle greater than 90 degrees, and scalene triangles where all sides and angles are different.
It is a fundamental property that the sum of the angles in any triangle is 180 degrees. Thus, if all three angles are less than 90 degrees, their sum will not exceed 180 degrees, fitting the definition of an acute-angled triangle.
An acute-angled triangle has all three angles measuring less than 90 degrees. In an acute-angled triangle, all angles are less than 90 degrees, which means none of the angles are right angles (90 degrees) or obtuse angles (greater than 90 degrees).
A scalene triangle is a triangle with all three sides of different lengths, but it can still have angles measuring less than 90 degrees.