Yes, I think something like that, if you slice (the way described) a cone in two pieces the plane section will look like a triangle, I think the most important thing in this case is trying to imagine it.
Since I can't draw the picture I am given, I will describe the nature of the problem to see if anyone can help me out. I am given a solid, right circular cone. The cone is sliced perpendicular to its base through its vertex and the center of its base. Then I am asked which of the answer choices best represents the plane section (The section that is cut is shaded. So the plane section is the section of the cone that hasn't been cut, I assume.) The answer is what looks like a triangle (kind of like a flattened cone, one-dimensional). Does anyone know why this is the answer? My only guess is that after the cone was cut, they "flattened the edges out" and it looked like a triangle, but I'm a bit confused.
I read the link.. I understand how the "front" of the cross section would look like a triangle.. That is evident. But I don't understand what happens to the "back side of it," the 3-dimensional side, that would make the whole object a flat triangle.