Question 758661
Find the gradient of BC
Formula: y2 - y1/x2 - x1
         11-(-1)/4 - 6
             12/-2
              -6
As an altitude is at right angles
to the line it emerges from, the 
gradient of the line BC and the
gradient of the altitude will
multiply together to give -1
      m1 x m2 = -1
So, if the gradient of BC is -6
then the gradient of the altitude
is 1/6.
Setting up the equation:
Using y - b = m(x - a) with m = 1/6    Coords of A (2,1)
      y - 1 = 1/6(x - 2)
      y - 1 = 1/6x - 2/6
          y = 1/6x - 2/6 + 6/6 (1)
          y = 1/6x + 4/6
This is the equation but you can 
multiply through by 6

          6y = x + 4
Hope this helps.
:-)