show that the line A(-6,4),(-2,12),(0,1) are the vertices of a right triangle.

m1 = 12 - 4 / -2 + 6

    = 8/4

   = 2

m2 = 1-12/0+2

     = -11/2

m3 = 1-4 /0+6

      = -3/6

 m3 = -1/2

since the slope m3 = -1/2  and m1 = 2 are negative reciprocal of one another then they are perpendicular to each other and so they are vertices of a right triangle.