online help!

[rachael724]

Hey guys!

I am working on this problem

Evaluate dy/dt for the function at the point.

xy + x = 12; dx/dt = -3, x = 2, y = 5.

I have been searching the freemath.com site for help and I can not find anything that will help me, does anyone know where I can find this stuff?


Thanks a bunch!
Rachael

 

[pka]

\(\displaystyle \L
\frac{{dx}}{{dt}}y + x\frac{{dy}}{{dt}} + \frac{{dx}}{{dt}} = 0\).

Plug & chug.

 

[rachael724]

I am getting 9, is that wrong?

 

[pka]

\(\displaystyle \L
\begin{array}{l}
\frac{{dx}}{{dt}}y + x\frac{{dy}}{{dt}} + \frac{{dx}}{{dt}} = 0 \\
\left( { - 3} \right)\left( 5 \right) + \left( 2 \right)\frac{{dy}}{{dt}} + \left( { - 3} \right) = 0 \\
\end{array}\)

For the given problem 9 is correct!

 

[rachael724]

I am confused. I shouldn't plud -3 into dx/dt, right? Would it be 3?

 

[stapel]

Would it be 3?

Would what be "3"?

Please reply showing all of your steps and reasoning.

Thank you.

Eliz.