An obtuse-angled triangle is a triangle in which one of the interior angles measures more than 90° degrees. In an obtuse triangle, if one angle measures more than 90°, then the sum of the remaining two angles is less than 90°.
Here, the triangle ABC is an obtuse triangle, as ∠A measures more than 90 degrees. Since, ∠A is 120 degrees, the sum of ∠B and ∠C will be less than 90° degrees.
In the above triangle, ∠A + ∠B + ∠C = 180° (because of the Angle Sum Property)
Since ∠A = 120°, therefore, ∠B + ∠C= 60°.
Hence, if one angle of the triangle is obtuse, then the other two angles with always be acute.
An equilateral triangle can never be obtuse. Since an equilateral triangle has equal sides and angles, each angle measures 60°, which is acute. Therefore, an equilateral angle can never be obtuse-angled.
A triangle cannot be right-angled and obtuse angled at the same time. Since a right-angled triangle has one right angle, the other two angles are acute. Therefore, an obtuse-angled triangle can never have a right angle; and vice versa.
The side opposite the obtuse angle in the triangle is the longest.
In our surroundings, we can find many examples of obtuse triangles. Here are some examples:
Triangle shaped roofs
Hangars found in cupboards