# Homework Help: Can someone check if my derivative of this log function is correct? (exam in 6 hours)

1. Dec 14, 2009

### iamsmooth

1. The problem statement, all variables and given/known data
$$y = \log_{2}(x^2 + 1)$$

2. Relevant equations
I think the pattern is:

$$\frac{d}{dx}[\log_{b}(x)] = \frac{1}{x ln(b)}$$

3. The attempt at a solution

$$y\prime = \frac{2x}{(x^2+1)ln(2)}$$

I did this by applying the pattern (that may or may not be correct) and then chain ruling the middle. If this is correct, then would this amount of work be acceptable (as you can kind of eye it without doing much work)?

When we do weird functions like $$y=x^x^2$$ I know how to do them by taking the ln of both sides and playing around with log properties, since this is the only kind of question that came up on quizzes, it's the only kind of log derivatives I'm familiar with.

Anyways, thanks.

2. Dec 14, 2009

### Staff: Mentor

3. Dec 14, 2009

### iamsmooth

Re: Can someone check if my derivative of this log function is correct? (exam in 6 ho

Is there a reason why the denominator log(2) instead of ln(2)?

ln(x) != log(x), no?

Thanks for the webpage, seems awesomely useful for future reference.

4. Dec 14, 2009

### Staff: Mentor

Re: Can someone check if my derivative of this log function is correct? (exam in 6 ho

First line below the derivative states "log(x) is the natural logarithm"...

5. Dec 14, 2009

### iamsmooth

Re: Can someone check if my derivative of this log function is correct? (exam in 6 ho

Oh whoops, sorry.

Thanks a lot, appreciate the timely help :D