So I have the following subspace
$r − s − 2t − u=0$
$−r + 2s + 5t + 2u=0$
$s + 3t + u=0$
$3r + s + 5u=0$
And I need to find the basis. I know that $r,s,t,u$ are all scalars. I was thinking of decomposing these equations into variables and numbers, but i am not sure.
How would i find the basis ? Could somebody help me? I was thinkig it might have something to do with the span.