The problem is as follows The perpendicular Distance ON from the origin to line L is p, and ON makes an angle α with the positive x-axis. Show that L has the equation x*cosα + y*sinα = p What I've done First I made a drawing from the text and I assume ON and P are the same thing. Then I thought "How do I derive the equation for a line from this information?" I could try the equation of a line (y2-y1)=m(x2-x1) and if i know that the slope of the line ON is tan(α), thn the slope of the perpendicular line must be tan(α+90). But from thereon I'm somewhat stuck.