## Summary To Appendix

1. Graphs are an essential tool of modern economics. They provide a convenient presentation of data or of the relationships among variables.

2. The important points to understand about a graph are: What is on each of the two axes (horizontal and vertical)? What are the units on each axis? What kind of relationship is depicted in the curve or curves shown in the graph?

3. The relationship between the two variables in a curve is given by its slope. The slope is defined as "the rise over the run," or the increase in Y per unit increase in X. If it is upward- (or positively) sloping, the two variables are directly related; they move upward or downward together. If the curve has a downward (or negative) slope, the two variables are inversely related.

4. In addition, we sometimes see special types of graphs: time series, which show how a particular variable moves over time; scatter diagrams, which show observations on a pair of variables; and multicurve diagrams, which show two or more relationships in a single graph.

Elements of Graphs horizontal, or X, axis vertical, or Y, axis slope as "rise over run" slope (negative, positive, zero) tangent as slope of curved line o

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