# Homework Help: Integral rational function

1. Mar 15, 2013

### whatlifeforme

1. The problem statement, all variables and given/known data
evaluate the integral.

2. Relevant equations

$\displaystyle\int {\frac{1}{secx+tanx} dx}$

3. The attempt at a solution
can i just do ln|secx + tanx| ??

2. Mar 15, 2013

### SammyS

Staff Emeritus
Probably not.

What's the derivative of ln|secx + tanx| ?

Write the tangent in terms of sine & cosine and the secant as the reciprocal of the cosine.

Last edited: Mar 15, 2013
3. Mar 15, 2013

### Staff: Mentor

No. You're making the same mistake you made in this thread: https://www.physicsforums.com/showthread.php?t=678488.

It is NOT TRUE that
$$\int \frac{dx}{f(x)} = ln|f(x)| + C$$

The above is true only if f(x) = x, which is certainly not the case here.