# Are these two integral formulas the same?

1. Sep 26, 2007

### frasifrasi

In my book, we were give:

int of tanx dx = - ln|cos x| + c

and later I cam across:

int of tanx dx = ln |sec x| + c

--should I use these interchangeably or what?

2. Sep 26, 2007

### D H

Staff Emeritus
What is the relation between $\cos x$ and $\sec x$?

3. Sep 26, 2007

### genneth

$$ln\left(\frac{1}{x}\right) = -ln x \quad \textrm{and} \quad \sec x = \frac{1}{\cos x}$$

So yes, you can use them interchangeably.