Slope From Two Points
Rise over run, measured between any two points on the line.
Concept
Slope is a rate of change
Slope answers: when x increases by 1, how much does y move? Positive slope climbs, negative slope falls, zero slope is flat.
Pick the two points in either order — as long as you keep the same order in the numerator and denominator, the sign comes out right.
m = (y₂ − y₁) / (x₂ − x₁)