In a right-angled triangle ABC (angle C is 90 degrees), angle A is twice the angle B

In a right-angled triangle ABC (angle C is 90 degrees), angle A is twice the angle B, the hypotenuse of AB is 18 degrees. Find the AC leg.

Given:
Right-angled triangle ABC,
angle С = 90 degrees,
angle A = 2 * angle B,
AB = 18.
Find the length of the AC leg -?
Solution:
1) Consider a right-angled triangle ABC.
We know that the sum of the degree measures of any triangle is 180 degrees. Consequently:
angle A + angle B + angle C = 180;
2 * angle B + angle B + 90 = 180;
2 * angle B + angle B = 90;
3 angles B = 90;
angle B = 90: 3;
angle B = 30 degrees;
2) In a right-angled triangle opposite an angle of 30 degrees lies a leg, which is half the hypotenuse. Then AC = 1/2 * AB;
AC = 1/2 * 18;
AC = 9.
Answer: AC = 9.