# absolute value for the ln function

I tried to execute this but could not figure out the absolute value sign correctly

```
c = var('c')
c=-0.999
N=(sqrt(1-c^2)/Pi)*[2.239539+(c/sqrt(1-c^2))*ln|(0.9*sqrt(1-c^2)-c*0.435889)/(0.9*sqrt(1-c^2)+c*0.435889)|+(1.8*sqrt(0.19)/(0.81-c^2)];N
```

I need help on the correct symbol for the absolute value for the ln function. Also, how am I to vary the value of c. I know is should use the command `for`

. Example `for c=0.999, 0.901, -0.999`

, then yield the value of `N`

.

Well...