In a circle, if a diameter bisects a chord (that is not a diameter), then:

The chord and the diameter are perpendicular.

Suppose that chord AB is bisected by a diameter, which interserct the chord at point C.

Now, focus on triangles OAC and OBC. They have:

So, they are congruent. In particular, this means that angles ACO and BCO are equal. Since they sum up to 180, each of them must be 90°, so the diameter is perpendicular to the chord.

okay wait before i answer, is this for your points on a graph?

answer: y=0 if that is what u r looking for