Read a coordinate pair in the order horizontal position, then vertical position. Use the same point order in both differences when calculating a gradient.
| Quantity | Calculation |
|---|---|
| Gradient of \(AB\) | \(m=\dfrac{y_B-y_A}{x_B-x_A}\), provided \(x_B\ne x_A\) |
| Length of \(AB\) | \(AB=\sqrt{(x_B-x_A)^2+(y_B-y_A)^2}\) |
A rising line has positive gradient; a falling line has negative gradient. A horizontal line has gradient \(0\). A vertical line has no defined gradient because its horizontal change is zero.
Distance is always nonnegative. Gradient is a signed ratio, so a negative gradient does not mean a negative distance.
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