Hi,

 

[math]3x/(x^2+4)[/math]

 

I want to find the derivative of this but I can't use the quotient rule. So I figure I'll use the chain/product rule.

I'm new to calc though.

Do I use both? Or just one?

 

[math]= 3x(x^2 +4)^-1[/math]

[math]=-3x(2x(x^2+4)^-2[/math]

 

That's the chain rule I think.

Do I go on to use the product rule?

Edited January 19, 201213 yr by sysD

You need to use both (you used the chain rule properly to get one term) - add in the term containing the derivative of 3x.

I want to find the derivative of this but I can't use the quotient rule. So I figure I'll use the chain/product rule.

 

The quotient rule is just a special case. And, exactly why can't you use it?

The quotient rule is just a special case. And, exactly why can't you use it?

 

His ruler is broken ?

Hi,

 

[math]3x/(x^2+4)[/math]

 

 

[math]= 3x(x^2 +4)^-1[/math]

[math]=-3x(2x(x^2+4)^-2[/math]

 

That's the chain rule I think.

Do I go on to use the product rule?

 

Hi,

You can use the product and chain rule together. Remember the product rule says to differentiate [math]3x[/math] and keep [math](x^2 + 4)^-1[/math] and continue the procedure (which can be found in any Calculus Textbook) and also remembering the chain rule when differentiating [math](x^2 + 4)^-1[/math]

 

Now, [math]=-3x(2x(x^2+4)^-2[/math] this is one of the terms but you're missing one more term to get the answer

NB: Using the quotient rule is more direct!

 

Hope this helps!