Concept question-exponential function derivatives (calc II)

1. Sep 10, 2007

frasifrasi

Concept question--exponential function derivatives (calc II)

Ok, so there is an example on my textbook that asks for the derivative of y = x^2.

--after applying ln on both sides, if finally gets to the lny = xlnx step.

But after this step, it just states y'/y = x(1/x)+ lnx(1). I understand it is just the prod. rule on the right, but can anyone explain why it went from lny to y'/y ? Is this a property or formula that they used?

Thank you.

2. Sep 10, 2007

bob1182006

they used implicit differentiation on the lhs.

You might remember using it on things like xy=1 or equations like that in Calc I.

so (ln y)' = 1/y * dy/dx which gives the y'/y

3. Sep 10, 2007

Hurkyl

Staff Emeritus
Chain rule?

4. Sep 10, 2007

frasifrasi

Oh, I see. Thank you.