Characteristics of Triangles

A. Classified by side length

 1. Isosceles triangle

- Two sides of the triangle have equal length.

- The two base angles are equal.

2. Equilateral triangle

- All three sides have equal length.

- Its each angle is 60°.

3. Scalene triangle

- All three sides have unequal lengths.

B. Classified by angle size

1. Acute-angled triangle

All three angles are less than 90°.

2. Obtuse-angled triangle

One of the angles is more than 90°.

3. Right-angled triangle

One of the angles is exactly 90°.

Source: Mathematics Matters (Normal Textbook of Secondary 2, published by EPB Pan Pacific Singapore).