IF i have a T-invariant subspace U with dim \geq 3 containing the vector

v=
| -2 4 |
| 4 -2 |

with basis B=
| 1 0 |, | 1 1 |, | 1 1 |, | 1 1 |
| 0 0 | | 0 0 | | 0 1 | | 1 1 |

And M_B(T) =
| 7 8 2 -8 |
|-3 -4 -2 8 |
|-3 -6 -5 -5 |
| 1 1 5 12 |
And i need to find a basis for the T-invariant subspace, how do i approach this..

Ive been trying to find T(u)..

but i dont know where im screwing up.. ive been using this.. C_B(T(u))=M_B(T)C_B(u) to get to T(u)

witt C_b(u)=
| a+ b +c +d|
| b+c+d |
| d |
| c+ d |