Integrate:

f (x)/(2x + 1) dx

let f represent integrate sign

let u = x, du = dx => dx = du

= f (u)/(2u + 1) du
= (2u + 1)^(-1) du
= (1/2)u^2 (ln|2u + 1|) + c
= (1/2)x^2 (ln|2x + 1|) + c

...what did I do wrong? The correct answer is

(1/2)x - (1/4)ln|2x + 1| + c

It seems like there was a mistake made during the integration process. Let's go through the steps again and identify the error.

Starting from the initial expression:

∫f(x)/(2x + 1) dx

We can begin by letting u = 2x + 1. This allows us to rewrite the integral in terms of u:

dx = du/2

Now, substituting u and dx back into the integral:

∫f(x)/(2x + 1) dx = ∫f(x)/(u) (du/2) = (1/2) ∫f(x)/u du

Here is where the issue arises. Instead of integrating directly with respect to u, you integrated with respect to x, treating u as a constant. This led to an incorrect result in the solution.

To carry out the integration correctly, we should consider u as a variable and integrate with respect to u. Let's continue the correct steps:

∫f(x)/(2x + 1) dx = (1/2) ∫f(u)/u du

Now, this form of the integral can be integrated using standard techniques. However, without knowing the specific form of f(x), it is challenging to provide a more precise answer.