i got a set of linear equations with x,y,z,t variables. x=4,y=-2,z=-2,t=4 is a solution x=-2 y=4 z=4 t=-2 is a solution x=2,y=2,z=2,t=2 is not a solution. prove that this set is not homogeneous ? prove that x=0,y=2,z=2,t=0 is a solution? ??