I would think the easiest way of doing that is to take x = 2 as the cutting line and you will see that the first half is identical to the second half.


When x = 1 y = 1

which means when x is 1 point away from 2 on the x-axis, it is also 1 point away from the y-axis.

when x = 3, it is also 1 point away from the x-axis and so it should also be 1 point away from the y-axis.


basically my point is that the parabola is symmetric. any point on one side will be directly proportional to the other side.