How to find the coordinate vector x with respect to the basis B for R^3? 
Find the coordinate vector of $x = \begin{bmatrix}-5\\-2\\0\end{bmatrix}$ with respect to the basis $B = \{ \begin{bmatrix}1\\5\\2\end{bmatrix}, \begin{bmatrix}0\\1\\-4\end{bmatrix}, \begin{bmatrix}0\\0\\1\end{bmatrix} \}$ for $\mathbb{R}^3 $
$[x]_B = ?$

So I think I have an idea, but i'm not quite sure.. Should I just put this in matrix form and then put it in RREF form?

Basically I found that you need to just Put the Basis B matrices together with the vector x at the end and you get $[x]_B = \begin{bmatrix}-5\\23\\102\end{bmatrix}$
