Example: A triangle with one obtuse angle and two sides equal.
- A triangle is a 3 sided polygon.
- Triangles are two-dimensional figures.
- Triangles can be classified according to the relative lengths of their sides as:
- Equilateral triangle (3 sides of equal length)
- Isosceles triangle (two sides are of equal length)
- Scalene triangle (all sides have different lengths)
- Triangles can also be classified according to the their internal angles as:
- Right triangle (or right-angled triangle) has one 90° internal angle (a right angle). The side opposite to the right angle is the hypotenuse; it is the longest side in the right triangle. The other two sides are the legs of the triangle.
- An obtuse triangle has one internal angle larger than 90° (an obtuse angle).
- An acute triangle has internal angles that are all smaller than 90° (three acute angles).
- An equilateral triangle is an acute triangle, but not all acute triangles are equilateral triangles.
- An oblique triangle has only angles that are smaller or larger than 90°. It is therefore any triangle that is not a right triangle.
- The angles of a triangle add up to 180 degrees.
- The sum of the lengths of any two sides of a triangle always exceeds the length of the third side. That is called the triangle inequality.
Answer: Acute Isosceles triangle
Directions: Read the questions carefully and identify the type of triangle. Also draw an acute, obtuse, right, scalene, isosceles, equilateral triangle and show its properties.