Coordinate geometry equations

distance between two points = √(x₂ - x₁)² + (y₂ - y₁)²

(square root the whole equation)

x₁ + x₂   y₁ + y₂

______ , ______           = coordinates of the midpoint in brackets

    2            2

y₂ - y₁   

______         = gradient of straight line

x₂ - x₂

y - y₁ = m(x - x₁)       = equation of a straight line (or y = mx + c or ax + by + c = 0)