# Linear Algebra@Chapter 2

Tips before start:

• $I_{2}$ is identity matrix with 2x2 size, i.e. $\begin{bmatrix}1 &0 \\ 0 & 1\end{bmatrix}$

•  matrix A is n x m, matrix B is a x b. AB has size n x b, m must equal a, since A is coefficient matrix, B is vector of variables, each variables get one coefficient (a column), so # of column in A = # of row in B.
•  # of row in A is # of equation in the system, # of column in B is the # of column in the final matrix since each Ab will sum to one column

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