There are two main systems for measuring angles: the degree system and radian system. The degree system divides a full rotation into 360 equal degrees, while the radian system defines an angle as the arc length cut out on a unit circle. There are also two important types of right triangles used in trigonometry: the 45-45-90 triangle where the two legs have length a and the hypotenuse has length a√2, and the 30-60-90 triangle where one leg has length a, the other has length a/2, and the hypotenuse has length 2a.