Assuming you have an endpoint A = (x₁, y₁) and midpoint M = (x, y): Double midpoints' coordinates: 2x, 2y. Subtract the x-coordinate of the known endpoint from the first value to get the x-coordinate of the missing endpoint: x₂
To find midpoint you add your points and divide by two, so to find an endpoint you only need to do the opposite, double the midpoint and subtract the endpoint: x-value: 5 (2) - 2 =