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What's Wrong With My Answer?

by moe darklight
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moe darklight
#1
Dec1-08, 11:19 AM
P: 411
1. The problem statement, all variables and given/known data

y = (3x)^x

(find y' )

2. Relevant equations

y = a^x
y' = (a^x)(ln(a))

and the chain rule

3. The attempt at a solution

3((3x)^x)(ln(3x))
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rock.freak667
#2
Dec1-08, 11:31 AM
HW Helper
P: 6,208
Take ln of both sides of the equation

lny=x*ln(3x)

Now use implicit differentiation
moe darklight
#3
Dec1-08, 11:34 AM
P: 411
yes, that was the answer that was provided; but I don't understand why my answer is incorrect, given the fact that the derivative of a^x is (a^x)(lin(a)) and the formula seems to be of that form.

rock.freak667
#4
Dec1-08, 11:36 AM
HW Helper
P: 6,208
What's Wrong With My Answer?

I believe for that equation to work 'a' must be a constant.
moe darklight
#5
Dec1-08, 11:51 AM
P: 411
O, thanks.


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