You find the slope of line 5x-2y-8..then slope of line (l) × slope of line 5x-2y-8= -1.. You find the slope of (l).. Then (l) : y-yO=slope(x-xO) Then you substitute..
The question is unclear, so I'm going to go with this being the original question: 5x-2y=8 From this starting point we can rearrange to find the gradient of the line. y= (5/2)x +4
Therefore the line l, has gradient -2/5, from here we can see that the line must have equation y = (-2/5)x