## Precalculus (6th Edition) Blitzer

The solution set is $\left\{ \left( -5,-1 \right) \right\}$.
By rewriting the system as: \begin{align} & x-y=-4 \\ & x+4y=-9 \end{align} We subtract the second equation from the first equation to obtain: \begin{align} & x-y-x-4y=-4-\left( -9 \right) \\ & -5y=-4+9 \\ & -5y=5 \\ & y=-1 \end{align} Substitute the value of y in the first equation and solve for x: \begin{align} & x-\left( -1 \right)=-4 \\ & x+1=-4 \\ & x=-4-1 \\ & =-5 \end{align}. Thus, The solution set is $\left\{ \left( -5,-1 \right) \right\}$.