Math Is Fun Forum

nevinsmith

Member

Registered: 2010-05-19

Posts: 39

product rule problem

hi guys, so i understand that the product rule can be applied

when finding dy/dx for-       

y=f(x)g(x)

then dy/dx=f'(x)g(x)+g'(x)f(x)

but what happens if you are trying to find dy/dx for

y=f(x)f(u)

where u is a function of x as well?

for example y=f(x) (ln g(x))

do you use chain rule or is it just the same thing?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,158

Re: product rule problem

hi nevinsmith

You will have to use both the product rule (first) but also the chain rule when you come to

Example.

First product rule

Looking this over, I can see that simplifying the 'ln' would have been easier, but, so what, it's the method you wanted.

Hope that helps.

Post an question if you need further assistance.

Bob

Last edited by Bob (2011-02-11 21:42:05)

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Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

nevinsmith

Member

Registered: 2010-05-19

Posts: 39

Re: product rule problem

thanks for your help bobby now i understand!

Bob

Administrator

Registered: 2010-06-20

Posts: 10,158

Re: product rule problem

hi nevinsmith

You're welcome. 

Bob

---

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob