Help understanding the chain rule to solve a differential equation
I am following an example on a text book where the author is solving the next equation:
dp/dt = (p-900)/2
or if p is different than 900,
1/(p-900)dp/dt = 1/2 (so far so good for me)
But here the author states that by the chain rule the right hand side of the last equation is the derivative of ln|p-900| with respect to t:
d/dt (ln|p-900|) = 1/2
I really do not understand this last step. Any help will be very much appreciated :)
The reference of the book is: Boyce, DiPrima "Elementary Differential Equations"
Re: Help understanding the chain rule to solve a differential equation
If you were to differentiate $\displaystyle \displaystyle \begin{align*} \ln{\left| p - 900 \right|} \end{align*}$ with respect to t, remembering that p is a function of t, we have
$\displaystyle \displaystyle \begin{align*} \frac{d}{dt} \left( \ln{ \left| p - 900 \right| } \right) &= \frac{d}{dp} \left( \ln{ \left| p - 900 \right| } \right) \frac{dp}{dt} \\ &= \left( \frac{1}{p - 900} \right) \frac{dp}{dt} \end{align*}$
Re: Help understanding the chain rule to solve a differential equation
Now it is clear for me. Thanks "Prove it"