**Equilateral** – All sides are equal in length. All angles are 60°.**Isosceles** – Two sides are equal. Two angles are equal. If one angle is 90°, it is a right triangle, also.**Scalene** – No sides are equal. No angles are equal. One angle may be obtuse, or more than 90°.**Right** – No sides or two sides are equal. If two sides are equal, it is an isosceles triangle, also. The side opposite the right angle is called the hypotenuse. One angle is 90°, or a right angle.

**Right triangle ratios**

- Sine = opposite / hypotenuse
- Cosine = adjacent / hypotenuse
- Tangent = opposite / adjacent
- Cotangent = adjacent / opposite
- Secant = hypotenuse / adjacent
- Cosecant = hypotenuse / opposite

**Acute angle** – One that contains less than 90°**Right angle** – One that contains 90°**Obtuse angle** – One that contains more than 90°, but less than 180°**Straight angle** – One that contains 180°**Obtuse angle** – One that contains more than 90°, but less than 360°