根据OB=OA,180-3x=2x,x=36

5*x=180

不要以为角aob是直角

In triangle OAB , Angle O + Angle A + Angle B = 180 -------1
OA = OB (Radius) => Angle A = Angle B
In triangle ACB, Angle C = Angle O + Angle OAC (Sum of interior opposite angles)
=> Angle ACB = 2x;
Also, AC = AB => Angle ACB = Angle ABC = 2x each
Thus Angle A = Angle B = 2x each.
So, substituting in 1
5x = 180 => x = 36 deg.

求大神讲解，多谢

题图已更新。

https://gmatclub.com/forum/in-the-figure-above-point-o-is-the-center-of-the-circle-and-107874.html
图在这里

没有图啊。。。。