Chapter 1.1, Problem 31E

Each of lines $\left(\text{A}\right)\text{, }\left(\text{B}\right)\text{, }\left(\text{C}\right)\text{, and }\left(\text{D}\right)$

in the figure is the graph of one of the equations $\left(\text{a}\right)\text{, }\left(\text{b}\right)\text{, }\left(\text{c}\right)\text{, and }\left(\text{d}\right)\text{.}$

Match each equation with its graph.

$\begin{array}{cccccc}\text{a}\text{.}& x& +& y& =& 1\\ \text{b}\text{.}& x& -& y& =& 1\\ \text{c}\text{.}& x& +& y& =& -1\\ \text{d}\text{.}& x& -& y& =& -1\end{array}$