Read the result
The tool first finds the gradient, then anchors that gradient at one of the points. The final equation is just that movement rule written in algebra.
Coordinate geometry
Line Through Two Points
Build the equation of the unique straight line through two points, including vertical-line cases.
Formula
y - y1 = ((y2 - y1) / (x2 - x1))(x - x1)
Result
Worked substitution
Two distinct points determine exactly one straight line.
Where it helps
Use it for modelling a straight trend, setting up simultaneous equations, or turning measured points into a line you can substitute into.
Common slip
If both points are identical, there is no unique line. You need a second distinct point or a gradient.
Try it
Enter two points with the same y value. The answer should become a horizontal line; check that the gradient is 0.