Detail solution
Given the system of equations
$$2 x + y = -10$$
$$6 x + 3 y = -30$$
Let's express from equation 1 x
$$2 x + y = -10$$
Let's move the summand with the variable y from the left part to the right part performing the sign change
$$2 x = - y - 10$$
$$2 x = - y - 10$$
Let's divide both parts of the equation by the multiplier of x
$$\frac{2 x}{2} = \frac{- y - 10}{2}$$
$$x = - \frac{y}{2} - 5$$
Let's try the obtained element x to 2-th equation
$$6 x + 3 y = -30$$
We get:
$$3 y + 6 \left(- \frac{y}{2} - 5\right) = -30$$
so
is always executed
Gaussian elimination
Given the system of equations
$$2 x + y = -10$$
$$6 x + 3 y = -30$$
We give the system of equations to the canonical form
$$2 x + y = -10$$
$$6 x + 3 y = -30$$
Rewrite the system of linear equations as the matrix form
$$\left[\begin{matrix}2 & 1 & -10\\6 & 3 & -30\end{matrix}\right]$$
In 1 -th column
$$\left[\begin{matrix}2\\6\end{matrix}\right]$$
let’s convert all the elements, except
1 -th element into zero.
- To do this, let’s take 1 -th line
$$\left[\begin{matrix}2 & 1 & -10\end{matrix}\right]$$
,
and subtract it from other lines:
From 2 -th line. Let’s subtract it from this line:
$$\left[\begin{matrix}6 - 2 \cdot 3 & \left(-1\right) 3 + 3 & -30 - - 30\end{matrix}\right] = \left[\begin{matrix}0 & 0 & 0\end{matrix}\right]$$
you get
$$\left[\begin{matrix}2 & 1 & -10\\0 & 0 & 0\end{matrix}\right]$$
In 1 -th column
$$\left[\begin{matrix}2\\0\end{matrix}\right]$$
let’s convert all the elements, except
1 -th element into zero.
- To do this, let’s take 1 -th line
$$\left[\begin{matrix}2 & 1 & -10\end{matrix}\right]$$
,
and subtract it from other lines:
It is almost ready, all we have to do is to find variables, solving the elementary equations:
$$2 x_{1} + x_{2} + 10 = 0$$
$$0 - 0 = 0$$
We get the answer:
$$x_{1} = - \frac{x_{2}}{2} - 5$$
where x2 - the free variables