Find the value of k so that the graphs of 8y=kx-4 and 6x+24y=12 are perpendicular.

kx= 4
// Solve equation [1] for the variable  x  
  [1] 6x = 24y - 30 [1] x = 4y - 5// Plug this in for variable  x  in equation [2]
  [2] -12•(4y-5) - 24y = -36   [2] - 72y = -96 // Solve equation [2] for the variable  y  

  [2] 72y = 96    [2] y = 4/3 // By now we know this much :  x = 4y-5   y = 4/3// Use the  y  value to solve for  x  
  x = 4(4/3)-5 = 1/3 Solution : {x,y} = {1/3,4/3}