Possible Duplicate:
Exercise review: perpendicular-to-plane line
I have a plane in affine space in $\Bbb R^4$ described by two following equations:
\begin{Bmatrix}x+y-2z+q +2=0\\ -x-2y+3z+q=0\end{Bmatrix}
I have the coords of a point $P$: (1,2,3,4).
I have to describe the locus of all points $Q$ such that line $PQ$ is $\bot$ to the plane.