Geometry and Discrete Mathematics (Matrix)

[Cyto]

Hey all, i'm having some problems with this one homework question... We just did The Intersection of Three Planes using The augmented matrix... and heres my question...

For what value of k will the following set of planes intersect in a line?

x - 2y - z = 0
x + 9y - 5z = 0
kx - y + z = 0

[HallsofIvy]

Try solving the thre simultaneous equations. The solutions will, of course, involve k. Find a value of k for which you do NOT get a single value (that would probably be a value of k that makes a denominator 0.)