Does anyone know of any interactive/good visual website for the adding and subtracting of planes? I'm doing the intersection of 2 planes right now, and I was just wondering if you had 2 cartesian eq'ns say 5x+2y+7z+1=0 and 5x-6y+8z-1=0, if you minus the 2 equations you'll have eliminated x, and you'll get a line equation with only y and z as the variables. I'm just trying to get a visual idea of what's going on when you eliminate a variable from 2 cartesian equations. So originally you had two different planes, now that you subtracted one from the other, what does the new line represent? If any one can help explain it/provide visual that would be greatly appreciated.