In this exercise, we need to classify the slope of each line in the four graphs as "zero," "undefined," "positive," or "negative."

Here’s the classification based on each graph from left to right:

1. First graph: The line rises from left to right, which means it has a positive slope.
2. Second graph: The line falls from left to right, which means it has a negative slope.
3. Third graph: The line is horizontal, meaning there is no change in the $y$-value as $x$ changes, so it has a zero slope.
4. Fourth graph: The line is vertical, meaning there is no change in the $x$-value as $y$ changes, so it has an undefined slope.

So, in the boxes above each graph, we would write:

1. Positive
2. Negative
3. Zero
4. Undefined

Would you like more details on why each slope is classified this way?

Related Questions

1. What is the formula for calculating the slope between two points?
2. How does a zero slope differ visually from an undefined slope?
3. Can the slope of a line be both zero and undefined at different points?
4. How can you determine the slope just by looking at a line's direction?
5. What is the real-world significance of positive and negative slopes?

Tip: Remember that horizontal lines always have a zero slope, while vertical lines always have an undefined slope!