Slope is rise over run. On ACT Math, that is the change in y divided by the change in x. There is no formula sheet. Slope sits with the other coordinate tools in coordinate geometry.
From two points
For points (x1, y1) and (x2, y2), slope is (y2 − y1) / (x2 − x1). A line through (1, 2) and (4, 8) has slope (8 − 2) / (4 − 1) = 2. A horizontal line has slope 0. A vertical line has an undefined slope, because the run is 0.
In slope-intercept form, y = mx + b, the m is the slope and b is the y-intercept. If the line is written as Ax + By = C, solve for y before you read the slope.
What slope tells you next
Parallel lines share a slope. Perpendicular lines have slopes that multiply to −1. That case is in parallel and perpendicular lines. The formula list is in ACT Math formulas. Lines and angle measures, which are not the same as slope, are in lines and angles.
The bottom line
Subtract the y-values, subtract the x-values in the same order, and divide. Watch for a zero in the denominator.
Start practicing
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