1. ## Derivative problem?

Could someone help me with this problem. I am coming up with 1/((sqrt(4x^2-1))+1) and it is wrong. Thanks

2. Hello,
Originally Posted by johnny4lsu
Could someone help me with this problem. I am coming up with 1/((sqrt(4x^2-1))+1) and it is wrong. Thanks

You didn't use the chain rule !

$[f(g(x))]'=g'(x) f'(g(x))$

Here, it gives :
$[\tan^{-1}(u(x))]'=u'(x) \cdot \frac{1}{(u(x))^2+1}$

Do you understand ?

3. let me try again moo! thanks

4. i'm still can't figure it out Moo!! Could you walk me through it!

5. Originally Posted by johnny4lsu
i'm still can't figure it out Moo!! Could you walk me through it!
Okay !

First, you should calculate the derivative of u(x), namely $\sqrt{4x^2-1}$
You'll have to use the chain rule once again !

That is $(\sqrt{v(x)})'=\frac{v'(x)}{2 \sqrt{v(x)}}$

$u'(x)=\left(\sqrt{4x^2-1}\right)'=\frac{8x}{2 \sqrt{4x^2-1}}=\frac{4x}{\sqrt{4x^2-1}}$

Does it help ?

If not, I'd suggest you have a look here : Chain rule - Wikipedia, the free encyclopedia

6. Thanks a lot moo!!! I figured it out!!