x1:N(-100,100), x2:N(-100,100), x3:N(-100,100), x4:N(-100,100)
(((((((x1 - 1) * (x1 - 1)) + (x2 * x1)) - ((x2 - 1) * (x2 - 1))) + (x3 * x2)) - ((x3 - 1) * (x3 - 1))) + (x4 * x3)) - ((x4 - 1) * (x4 - 1))
