# Parabolics questionWatch

#1
1). The rectangular hyperbola H has equation xy = c^2

The points P (cp, c/p) and Q (cq, c/q) lie on H

a) Show that the gradient of the chord PQ is -1 / pq

Ive done that, simple y diff/x diff standard!

b) The point R (3c, c/3) also lies on H and PR is perpendicular to QR. Show that this implies that the gradient of PQ is 9.

I dont get b). How do you show that?

ANY HELP?
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10 years ago
#2

-1/pq. The question is now asking you to show that this is going to be 9. This implies you're trying to show that pq = -1/9 (because -1/(-1/9) = 9).

Can you show that?

Hint

Spoiler:
Show
If PR is perpendicular to QR, then their gradients when multiplied = -1.
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