<s>[INST] How to find $a, b$ and $c$ from this system of linear equations? Find $a$, $b$ and $c$ from:
$$
\begin{align}
a+c &= 3 \\
b+a &= 2  \\
c+b &= -1 \\
\end{align}
$$
I tried the following way, the answer comes wrong:
$$(a+c) + (b+a) = 3+2$$
 [/INST] $$a+c=3.....(1)$$
$$b+a=2.....(2)$$
$$c+b=-1.....(3)$$
Try your way and solve like this-
$$(a+c)+(b+a)=3+2$$
$$2a+c+b=5.......(4)$$
Now, subtract equation(3) from (4)
$$ \begin{array}\ 2a+c+b=5 \\\;\;\;\;\;-c-b=1\\ \hline2a\;\;\;\;\;\;\;\;\;\;\;=6
 \end{array}$$
$$2a=6\;\implies a=3$$
Now, Put the value value of $a$ in equations(1) and (2)-
$$3+c=3\;\implies c=0$$
$$b+3=2\;\implies b=-1$$
I hope it'll help.
</s>