# How do you solve this system of equations: 7x + y = 11;- 10x - 5y = 20?

Feb 6, 2017

The method I am using is subsitution.

#### Explanation:

First, isolate x in the second equation as it is easier to do so;

$- 10 x = 20 + 5 y$

$x = - 2 - 0.5 y$

Then, replace x in the first equation with the equation above;

$7 \left(- 2 - 0.5 y\right) + y = 11$

$- 14 - 3.5 y + y = 11$

$- 2.5 y = - 25$

$y = - \frac{25}{-} 2.5$

$y = - 10$

Now we know y equals to -10

Now, substitute this value to y of the second equation

$- 10 x - 5 \left(- 10\right) = 20$

$- 10 x + 50 = 20$

$- 10 x = 20 - 50$

$x = 3$

And x equals to 3