The direction vectors for the three sides are given by the differences in the vertices, not the vertices themselves. So consider the vectors P−Q,P−R,Q−RP−Q,P−R,Q−Rand see whether any of these are orthogonal.
you should know you dont need help so do it by yourself. if you want the awnser you should know or you just dont pay attention in class.1234567890 is your awnser
