Types of triangles
Triangles can be classified by their sides or by their angles. According to these, we can assert that there are basically six different types of triangles: equilateral triangle, isosceles triangle, scalene triangle, right triangle, acute triangle, and obtuse triangle.
By Side
- Equilateral Triangle: All three sides are equal. Therefore, its three angles are also equal. That is to say:
Since all angles are equal and add up to 180° (why do angles add up to 180°?), they are all 60° α=β=γ=60°.
- Isosceles Triangle: It has two equal sides. Hence, it also has two equal angles.
As we see in the image above, the unequal angle β is the one formed by the two equal sides (a and c).
- Scalene Triangle: All three sides are unequal, so their three angles are different too from each other. Therefore, we have that:
By Angle
- Right Triangle: It has one angle equal to 90 degrees. The other two are acute angles, i.e. they measure less than 90 degrees.
- Oblique Triangle: It hasn’t any angle measuring 90 degrees. Oblique triangles can be classificated in:
- Acute Triangle: all three angles are acute, that is, its angles measure less than 90°.
- Obtuse Triangle: One of its angles is greater than 90°. The other two are acute (less than 90°).
Summary: Types of Triangles
The table below shows the different types of triangles based on sides and angles:
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