Measure the interior angles of the triangle using a protractor. If all the three angles are acute (less than 90 degrees), the triangle is an acute-angled triangle.
On measuring the interior angles of the triangle, if one angle is obtuse (greater than 90 degrees) and other two angles are acute, it is an obtuse-angled triangle.
Measure the interior angles of the triangle. If one of the interior angle measures exactly 90 degrees (a right angle and the other two angles are acute), the triangle is a right-angled triangle. The side opposite to the right angle is the longest side of the triangle and is called as hypotenuse.
On measuring the interior angles of the triangle, if all the three angles are equal to 60 degrees, it is called as equilateral triangle or equiangular triangle. It is also called as a regular polygon.
Measure the interior angle of the triangle. If only two angles of the triangle are equal, it is an isosceles triangle. The meaning of Isosceles is "equal legs." An isosceles triangle has two sides and two angles equal. This means that the two angles formed when two equal sides meet the third side are equal. A right angled triangle having two angles equal to 45 degrees is also an isosceles triangle.
Consider the triangle as scalene if all the interior angles and sides of the triangle are unequal. A right angled triangle having all the interior angles unequal can also be a scalene triangle.