For a 30-60-90 right-angled triangle, the sides are in the ratio 1 : √(3) :
2. The side opposite the 30° angle is the shortest (1), the side opposite the 60° angle is √(3) times the shortest, and the hypotenuse (opposite the 90° angle) is twice the shortest side. Here, the side opposite 30° is 2, so the hypotenuse (diameter) must be 2 × 2 = 4.