The value of the dependent variable (the "effect") is determined by the value of the independent variable (the "cause").

When the "other factors" that might affect a two-variable relationship are allowed to change, the graph of the relationship will likely shift to a new location.

6. The slope of a straight line is the ratio of the vertical change to the horizontal change between any two points. The slope of an upsloping line is positive; the slope of a downsloping line is negative.

7. The slope of a line or curve depends on the units used in measuring the variables. It is especially relevant for economics because it measures marginal changes.

8. The slope of a horizontal line is zero; the slope of a vertical line is infinite.

9. The vertical intercept and slope of a line determine its location; they are used in expressing the line—and the relationship between the two variables—as an equation.

10. The slope of a curve at any point is determined by calculating the slope of a straight-line tangent to the curve at that point.

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