It depends on what type of triangle you are dealing with, and also what you are meaning by what are they.
If you are just talking in general terms 2 are legs, and one is the hypotenuse.
In right triangles the hypotenuse is the side opposite the right angle, and the legs are adjacent to it.
A hexagon.
Trapezium
A triangle.
That is the definition of a triangle. If it did not have three sides it would not be a triangle. If it did not have three angles, it would not be a triangle.
A triangle.
A triangle with three sides is a polygon.
Its volume in cubic inches is 27.
An equilateral triangle is a triangle in which all three sides are equal. An example is a triangle with 60o in all three corners.
It impossible for a triangle to have three acute angles. * * * * * What? A triangle most certainly can have three acute angles. Such a triangle would be called an acute-angled triangle!
A triangle with three congruent angles
Three is to triangle as eight is to octagon.
a triangle is a polygon with three sides.