suppose..

**tbenne3** · March 1st 2010, 12:21 PM

yea i don't even know where to start on this problem...

Suppose

and

. Find

when

.

(dx/dt)=?

**skeeter** · March 1st 2010, 12:32 PM

Originally Posted by tbenne3

yea i don't even know where to start on this problem...

Suppose

and

. Find

when

.

(dx/dt)=?

$ \frac{d}{dt}\left(xy = 3\right) $

$ x \cdot \frac{dy}{dt} + y \cdot \frac{dx}{dt} = 0 $

take it from here?

**tbenne3** · March 1st 2010, 12:38 PM

Originally Posted by skeeter

$ \frac{d}{dt}\left(xy = 3\right) $

$ x \cdot \frac{dy}{dt} + y \cdot \frac{dx}{dt} = 0 $

take it from here?

is it -3?

**featherbox** · March 1st 2010, 12:53 PM

$\frac{dx}{dt}=\frac{dx}{dy}\frac{dy}{dt}$

**tbenne3** · March 1st 2010, 03:12 PM

**skeeter** · March 1st 2010, 03:50 PM

Originally Posted by tbenne3

this is not that difficult.

$xy = 3$

if $x = -3$ , then $-3y = 3$ ... $y = -1$

you were given $\frac{dy}{dt} = -3$ ... now use the derivative equation to solve for $\frac{dx}{dt}$

**tbenne3** · March 1st 2010, 03:53 PM

Originally Posted by skeeter

this is not that difficult.

$xy = 3$

if $x = -3$ , then $-3y = 3$ ... $y = -1$

you were given $\frac{dy}{dt} = -3$ ... now use the derivative equation to solve for $\frac{dx}{dt}$

sorry just not following.. what is the derivative of dx/dt

**skeeter** · March 1st 2010, 04:17 PM

$ x \cdot \frac{dy}{dt} + y \cdot \frac{dx}{dt} = 0 $

$(-3) \cdot (-3) + (-1) \cdot \frac{dx}{dt} = 0$

solve for the value of $\frac{dx}{dt}$

**tbenne3** · March 1st 2010, 04:41 PM

Originally Posted by skeeter

$ x \cdot \frac{dy}{dt} + y \cdot \frac{dx}{dt} = 0 $

$(-3) \cdot (-3) + (-1) \cdot \frac{dx}{dt} = 0$

solve for the value of $\frac{dx}{dt}$

thanks

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