1. The problem asks: Which graph has an undefined slope? 2. Recall the definition of slope: slope $m$ is the ratio of the change in $y$ to the change in $x$, or $$m=\frac{\Delta y}{\Delta x}.$$ 3. For a vertical line, the change in $x$ is zero ($\Delta x=0$), so the slope formula becomes $$m=\frac{\Delta y}{0},$$ which is undefined because division by zero is not allowed. 4. The graphs described are: - Top-left: positive slope (defined) - Top-right: negative slope (defined) - Bottom-left: horizontal line with slope 0 (defined) - Bottom-right: vertical line with undefined slope 5. Therefore, the graph with an undefined slope is the bottom-right graph, the vertical line. Final answer: The vertical line (bottom-right graph) has an undefined slope.