Drag the vertices around. Use the arrow keys to finely move the green (A) vertex (useful to draw equilateral triangles).
Vertices are constrained on a 10x10 grid. Sides' lenght is rounded to the unit.
NOTE: due to the rounding to the unit, sometimes it says that the triangle is degenerate (i.e. two sides add up to the third side) even if it is not really degenerate. This could be corrected by calcuting two separate lengths, one rounded and one exact for each side.