Economics · Ch 1 — Graphs in Economics

Slope of a Line

The slope of a line measures how much the variable on the Y-axis changes for a one-unit change in the variable on the X-axis — in other words, the rate of change of one variable with respect to the other.

m = \dfrac{\Delta y}{\Delta x} = \dfrac{y_2 - y_1}{x_2 - x_1}

where $(x_1, y_1)$ and $(x_2, y_2)$ are any two points on the line, and $\Delta$ ("delta") means "change in."

Reading the sign and size of a slope:

Slope	Shape of the line	Typical economic example
Positive ( $m > 0$ )	Rises left to right	Supply curve: price and quantity supplied move together
Negative ( $m < 0$ )	Falls left to right	Demand curve: price and quantity demanded move oppositely
Zero ( $m = 0$ )	Horizontal line	A perfectly elastic supply/demand at a fixed price
Undefined (vertical line)	Vertical line	A perfectly inelastic (fixed) quantity, whatever the price

Definition 1Slope

The rate of change of the Y-axis variable with respect to the X-axis variable, computed as m = (y2 …

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