Solution
= Solution
Multiplication of a <matrix> by a column <vector> forms the linear combination of its columns with coefficients from that <vector>. Here
$$
\boxed{\mathbf c_1=(1,1,2)^{\mathsf T},\quad\mathbf c_2=(\mu,-1,-2)^{\mathsf T},\quad\mathbf c_3=(0,3,\mu)^{\mathsf T},}
$$
so $A\mathbf r=x\mathbf c_1+y\mathbf c_2+z\mathbf c_3$. Equating this expression with $\mathbf b$ reproduces the original three <linear equations>.