Find the equation of the line through [1,2,-1] perpendicular to the plane ,the length of the perpendicular, and the coordinates of its foot
The parametric equations of the line l with parameter t is
The projection of on the plane is
The length of the perpendicular is
Let the straight line pass through the point and has direction-cosines (or ratios)
Define the line l1 that passes through and has as its direction-ratios
Define the line l which is the intersection of two given planes p1, p2