trshvn wrote:
Conceptually, if I were to give you a structure of the form ⊥ and ask that you complete the triangle, you’ll be forced to join the remaining two sides to the tip of the vertical line stretching out from the base. These remaining two sides must also fully extend to the endpoints of the base and so it follows from this logic that the lengths of your sides will be fixed, thus known. So, answer choice B is the correct answer for this question IMO.
That can be a good way to think about GMAT DS geometry questions, but it's important if you're doing this to recognize which features of the diagram are fixed and which are flexible. Here we don't know the position of the vertical line. It might be directly in the center of the line MO, in which case from Statement 2 the triangle will indeed be equilateral. But it might be off-center as well, and if it is, the triangle will not be equilateral.
We also don't even know that the vertical-looking line is actually vertical; the question would need to tell us explicitly that it is at 90 degrees to line MO. I'd bet the question writer intends for that line to be a height, just because they called it "h", but a line is not a height just because it's labeled with a particular letter. So we really know neither the position nor the angle of the vertical-looking line, and we can freely draw the diagram in all kinds of ways using Statement 2, one of which will make the triangle equilateral and the rest of which will not.