Two
4
There are 2 obtuse angles (greater than 90°) : the top and bottom of the X.
There are no triangles.
A triangle can have at most one obtuse angle, but triangles do not necessarily have any obtuse angles.
There are 8 triangles.
Two.
4
Their four triangles in the Jamaican flag
2 of them (the green triangles).
There are 2 obtuse angles (greater than 90°) : the top and bottom of the X.
There are no triangles.
21
A triangle can have at most one obtuse angle, but triangles do not necessarily have any obtuse angles.
Triangles do not have to have any obtuse angles but they can have one.
There are 8 triangles.
The least number of obtuse triangles, if all possible triangles are drawn for n points in a plane, is zero. If all the n points lie in a straight line, no triangles are possible and so no obtuse triangles are able to be drawn; thus for any number n, there is a possibility that no obtuse triangles can be drawn, so the least possible number of obtuse triangles drawn is zero.
All triangles have 3 sides.