I am trying to find the determinant of this matrix but was told by my teacher that we wouldn't need to find the determinant of more than $3\times 3$ matrices so I am guessing there is a way of solving this without knowing how to solve a proper $4\times 4$ matrix. I think its something to do with the zeros but not sure. Would be grateful for a hint at the right direction.
\begin{bmatrix} 1 & 0 & 0 & 1 \\ 0 & 1 & 0 & 1 \\ 0 & 0 & 1 & 1 \\ 0 & 0 & 0 & 1 \end{bmatrix}
by using the cofactor method the determinant becomes
see http://en.wikipedia.org/wiki/Minor_%28linear_algebra%29