bibas, its been a long while..i haven't done those stuf...so don't remember offhand....but general...your solutions should be easy. If you have four unknows...say w,x,y,z....all u got to do is find three equations....in terms of w,x,y...by equating all of them to z and solve using simulataneous equation. lets say u have sth like 7w+3x+4y-z=0.........(i) 6w+2x+10y-2z=0.......(ii) .......................... .......................... you can take like (i) and (ii), so that u will have sth like, 7w+3x+4y=3w+x+5y i.e.4w+2x-y=0...............(a)....Similarly u can find other three solutions...by taking two other equations out of the four....and solve the three unknowns using simulataneous equation. Hope that helps.