Look at the graph from left to right. As you do that, x is increasing. What's happening to y? It's getting larger--the points on the graph are getting higher and higher. That's positive slope: increasing x produces increasing y.
Negative slope occurs when x gets larger (move from left to right on a graph) and the values of y get <u>smaller</u> -- points on the graph get lower and lower. The graph falls from left to right.
Zero slope occurs when x gets larger and y <u>stays the same</u>. The graph is a horizontal line -- it does not rise or fall.
