Functions

**theflyingcow** · November 4th 2008, 10:42 AM

For each function f(x) find f'(x)

A) f(x) = log(1/2) x

the 1/2 is subscript.

I got the answer ln(x) / -ln(2).
Is this correct i don't feel confident in it.

**Moo** · November 4th 2008, 10:44 AM

Hello,

Originally Posted by theflyingcow

For each function f(x) find f'(x)

A) f(x) = log(1/2) x

the 1/2 is subscript.

I got the answer ln(x) / -ln(2).
Is this correct i don't feel confident in it.

Not really !
What you got is another expression for f :

$\log_{1/2}(x)=\frac{\ln(x)}{\ln(1/2)}=-\frac{\ln(x)}{\ln(2)}$

Treat $\ln(2)$ as a constant and then find the derivative !

MOOOOOOOOOOO

**theflyingcow** · November 4th 2008, 10:54 AM

How do I treat it as a constant. What I have is how far I am with keeping up with the teacher

**Moo** · November 4th 2008, 10:57 AM

Originally Posted by theflyingcow

How do I treat it as a constant. What I have is how far I am with keeping up with the teacher

If a is a constant, then the derivative of $a \cdot f(x)$ is $a \cdot f'(x)$

So $\left(-\frac{\ln(x)}{\ln(2)}\right)'=-\frac{1}{\ln(2)} \left(\ln(x)\right)'$

what's the derivative of the logarithm ?

**theflyingcow** · November 4th 2008, 11:03 AM

x / ln10 i believe

**Black Kawairothlite** · November 4th 2008, 02:31 PM

wrong mate the derivate of ln (x) is:

$\frac{{d}}{{dx}}ln (x)=\frac{{1}}{{x}}$

**theflyingcow** · November 4th 2008, 04:56 PM

so where do i go (-1/ln(2)) * (1/x)

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