# proportionality of rate of change

• Dec 28th 2012, 04:01 PM
zachd77
proportionality of rate of change
Doing another problem:

Show that the rate of change of Attachment 26390 is proportional to y.

I know that you have to find the derivative & somehow find a constant to place in front of y. ​Stuck here.
• Dec 28th 2012, 04:20 PM
skeeter
Re: proportionality of rate of change
Quote:

Originally Posted by zachd77
Doing another problem:

Show that the rate of change of Attachment 26390 is proportional to y.

I know that you have to find the derivative & somehow find a constant to place in front of y. ​Stuck here.

what did you get for the derivative of y ?
• Dec 28th 2012, 04:34 PM
zachd77
Re: proportionality of rate of change
I got 3^(2x)*(7 ln(5))5^(7x)+5^(7x)*(2 ln(3))9^x... bit messy, best I could do to show y'
• Dec 28th 2012, 04:40 PM
skeeter
Re: proportionality of rate of change
$y' = 3^{2x} \cdot 7\ln{5} \cdot 5^{7x} + 5^{7x} \cdot 2\ln{3} \cdot 3^{2x}$

$y' = 3^{2x}5^{7x}(7\ln{5} + 2\ln{3})$

$y' = y(7\ln{5} + 2\ln{3})$
• Dec 28th 2012, 05:42 PM
zachd77
Re: proportionality of rate of change
thanks!!