Question

how do you show that the set V of all 2x2 upper triangular matrices is a subspace of M(sub)22

Answer 1

To show V is a subspace of \(M_{22}\) you need to prove that V satisfies
1/ for all u, v in V, (u+v )\(\in \)V
2/k*u = ku
3/u+v = v+u
4/ u +0 = 0+u =u
5/u +(-u) =0
6/u*I = u

Answer 2

ok, I can try that, my brain is fried right now though...