1) for a valid triangle two sides added together have to always be larger than the third (otherwise it turns into a line)
12, 18, 6 would not be a valid triangle, because 12+6<=18 but 12, 18, 14 would be valid, because 12+18>14 12+14>18 18+14>12
2)lets start with an obvious right triangle and have the axis along the y and x axis like so decide some x like -4 and some y like -3 and keep all other coordinates at 0: A=(-4,0) B=(0,-3) and C=(0,0)
make it a bit more complicated (less 0s) by some x and y translation like (-2,3) just add that to every point's coordinates and you get
