Answer
The system has no solution
Work Step by Step
We first have to solve the equations for $y$.
$x+y=11$ Simplify
$y=-x+11$
$-x-y=11$ Simplify
$y=-x-11$
To solve the equation, we will use the table function of a graphing calculator. Input both of the equations as $y_1$ and $y_2$ and look for an $x$ value where both $y_1$ and $y_2$ are the same.
$y_1=-x+11$
$y_2=-x-11$
As the output shows, this system has no solution.
