The slope of a line indicates how much change occurred. Depending on what the line graphs in macroeconomics, the slope could show how quickly supply responds to demand or demand to price. More generally, the slope equals the rise over the run of the equation.
Choose two points along the line on the macroeconomics graph. For instance, if you graphed price and demand, with the prices on the y-axis (vertical) and the quantity demanded on the x-axis (horizontal), you can choose the following points: (5, $4) and (6, $2).
Subtract the y-values (prices) by taking the price amount of the second point with the smaller x- value from the price amount from the first point with the larger quantity demanded to find the change in price. For example: $2 - $4 = - $2. A negative number indicates that the slope decreases.
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Subtract the smaller quantity demanded from the larger x-value to find the change in quantity demanded. For the example: 6 - 5 = 1.
Divide the change in price (change in x) by the change in quantity demanded (change in y). For the example: -2/1 = -2. The slope of -$2 indicates that for every $2 the price increases, the quantity demanded decreases by one.