Prove that in a right-angled triangle one of the angles is 30 degrees if the leg is 2 times less than the hypotenuse.

Given:
right-angled triangle ABC;
angle C = 90;
AB = 2 * BC;
Prove that the angle A = 30 degrees.
Evidence:
Consider a right-angled triangle ABC.
The sine of the angle in a right-angled triangle is equal to the ratio of the opposite leg to the hypotenuse. Hence:
sin of angle A = BC / AB (since AB = 2 * BC);
sin of angle A = BC / 2 * BC (BC is reduced);
sin of angle A = 1/2 * 1;
sin of angle A = 1/2;
angle A = 30 degrees.
Q.E.D.