Since the two straight lines are vertical, the two vertical lines in the middle are also vertical.

Then their slope product is-1.

Since one slope is k, the other slope is (-1/k).

Two straight lines pass through the same point (p, 0), so any of their properties are only determined by the slope! !

So we just need to replace k in the conclusion with (-1/k).

Answer: -2pk-PK 3

PS: If it is a big problem, you can first find the coordinates of the midpoint of the chord by the point difference method, and then substitute it into the linear equation, and you can get it.