Geometry Derivative Show that the normals to the curve $y=4x^2$ from points the same distance on either side of the y-axis intersect on the y-axis.
My attempt, I differentiated so it becomes $8x$, but I don't understand the question. Can anyone explain it to me ? Thanks in advance: 

That parabola is symmetric with respect to $y$-axis, hence the normal lines issued from two symmetric points (as in your case) are corresponding one another through a reflection across $y$-axis. Unless they are both parallel (which is not possible if they are issued from different points) they must therefore meet on the $y$-axis.
