# Math Help - Cal. problem

1. ## Cal. problem

Suppose that a point is moving along the path xy=1
so that
dy/dt= 3.
Find dx/dt when x = 1.
dx/dt =?

2. dx/dt = dx/dy x dy/dt

Differentiate xy = 1 implicitly to find dx/dy

3. Originally Posted by Johnson
Suppose that a point is moving along the path xy=1
so that
dy/dt= 3.
Find dx/dt when x = 1.
dx/dt =?
You need to use a product rule $\frac{d}{dt}(xy)=\frac{d}{dt}(1)$

$\frac{dx}{dt}y + x\frac{dy}{dt} = 0$ (chain rule on the inside because this is with respect to t)

You are given x = 1 so then (1)(y)=1
y=1
substitute all the values in and solve for $\frac{dx}{dt}$ this is part of related rates if you'd like to read in your calculus textbook to clear up any thing you're confused about.

4. I just want an answer!
Thanks

5. Originally Posted by Johnson