Question 1140964
Look at the slopes of any two of the points and see if they are a negative reciprocal, which would mean perpendicular
AB has slope of -4/2
BC has slope of 2/-6 or -1/3
CA has slope of -2/-4 or +1/2
AB and CA have a negative reciprocal slope so perpendicular.

One can also use the distance formula for 
AB sqrt(4+16)
BC sqrt (36+4)
CA sqrt (4+16)
sum of the sqrts is 20+20=40, and that is a right triangle as well.