# Thread: Integration Question as Part of a Differential Equation

1. ## Integration Question as Part of a Differential Equation

I am posting this here because I don't need help on the whole DE just on this integral..

Here it is:

Please explain.. I can't come up with pi in the denominator..

2. Originally Posted by eingeist
I am posting this here because I don't need help on the whole DE just on this integral..

Here it is:

Please explain.. I can't come up with pi in the denominator..
Excause me, Did you try the substitution $u=\frac{-\pi}{x}$ ?

3. I see... Would I pull 1/pi out in front of the integral? Or would I simply pull pi out since du = pi/x^2...

Seems like it would have to be 1/pi to get that pi in the denominator.

4. Originally Posted by eingeist
I see... Would I pull 1/pi out in front of the integral? Or would I simply pull pi out since du = pi/x^2...

Seems like it would have to be 1/pi to get that pi in the denominator.
put $\pi$ inside the integral, and $\frac{1}{\pi}$ outside the integral.

Because they will cancel each other.
i.e. you just multiplied by 1.
See this:
$\int f(x) dx=\int (1) f(x) dx=\int \frac{\pi}{\pi} f(x) dx$
$=\int (\pi) (\frac{1}{\pi}) f(x) dx = \frac{1}{\pi} \int (\pi) f(x) dx$.

By the way, $du=\frac{\pi}{x^2} \;\ {\color{red} dx}$