1. The problem statement, all variables and given/known data Two coplanar lines, a and b are perpendicular to each other. a passes through the points (3,2,3) and (8,10,6). Find the equation for b if it passes through the point (7,49,25). 2. Relevant equations The equation were trying to find is r = [x,y,z] + s [x1,y1,z1] + t [x2,y2,z2] 3. The attempt at a solution Basically since the coordinates are perpendicular I used the cross product to find one direction vector. For my position vector I used (3,2,3). Now I'm not sure what to do with the last point (7,49,25) or what to do to find my second direction vector. I'm not even sure if I did the first part right. Help would be appreciated thanks! EDIT: I originally posted this in a different section but somebody told me it'd be better if I post it here. So if a mod could remove the other thread in the physics section that'd be awesome.