# Thread: natural log differentiating problem, thanks

1. ## differentiating (ln u)^(f) in x = a

I have to evaluate d/dx of (ln (5 – x^(2)))^(1/4) at x = 1

So, differentiating it I proceeded by y= (ln (5 – x^(2)))^(1/4) = ¼ (ln (5 – x^(2)))^(3-/4) * 1/(5 – x^(2)) * (-2x) = ¼ (ln (5 – x^(2)))^(3-/4) *(-2x)/(5 – x^(2));

By calculating this for x=1 gives me such a odd number, I am pretty sure I am wrong when I operate with the logarithmic values (since there I found after my mid-term that I have some gaps);

Could you take a look at it, and also give some links where I would be able revise some basic knowledge on logarithms?

Greatly appreciated,

2. ## Re: natural log differentiating problem, thanks

You should get $\displaystyle -\frac{1}{8(\ln{4})^\frac{3}{4}}$ or approximately -0.0978. Your derivative looks good (except you should have -3/4 instead of 3-/4).

- Hollywood

3. ## Re: natural log differentiating problem, thanks

oh, this was a typo (3-/4), but yes, thanks a lot - I was doing a dumb mistake - forgetting to multiply 1/4 from the first with the (-1/2) from the last, and just working with 4*(...) instead of 8*(...)

Thanks a lot