calculate the slopes
3-0 / -2 - 2 = 3/-4 = -3/4
3 - -4 / -2 - -1 = 7/-1 = -7/1
0 - -4 / 2 - -1 = 4/3
-3/4 and 4/3 are negative reciprocals so this is a right triangle
Answer is A
