Which triangles have one obtuse angle?

Answer 1

If the triangle has an obtuse angle then the other two angles must sum to less than 900.

The triangle therefore CANNOT be an equilateral triangle.

It CAN be an isosceles triangle with the two equal angles summing to less then 900.

For Example, 1200, 300, 300.

It could also be a scalene triangle with angles such as 1200, 500, 100.