Are you talking about the 20 17 national volume 3 science mathematics question 20?

Judging from the topic setting, this question means y^2 = 2x.

This is a parabola with a regular X shape.

At the same time, the L line intersects the parabola at two points.

Obviously, the slope of this L line cannot be zero, but it may not exist.

For a straight line whose k can't be 0, but it may not exist.

Let x=my+b be the basic mass ... where m= 1/k, and when k does not exist, m=0.

Of course, you can also choose to set y=kx+b as usual, and then add that if K doesn't exist, it doesn't meet the meaning of the question ... take another step!