Hi nahid078,
This question can be solved by TESTing THE ANSWERS, but you have to fill in some of the angles before you take that approach and you'll have to do a bunch of little calculations. I'm going to give you some hints, so that you can re-attempt this question on your own:
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1) Fill in the angles around the Origin.
2) Notice the Isosceles triangle with its "top" at the Origin? Fill in the two isosceles angles.
3) You now have one of the angles in the "little" triangle on the left. What do the OTHER 2 angles in it add up to? The angles OPPOSITE those two angles add up to the SAME total.
4) The large triangle with with one side as the diameter is a RIGHT triangle.
5) When you TEST THE ANSWERS, you now have 3 triangles that have to "add up" to 180: the big right triangle, the little right triangle and the smaller triangle with vertices at E and O. There's one value for X that will make all of those totals properly add up. You just have to do a bit or arithmetic now to find it.
[/spoiler]
GMAT assassins aren't born, they're made,
Rich
