How do you find the first and second derivative of (lnx)lnx?

1 Answer
Nov 11, 2016

y=(lnx)lnx

lny=ln(lnxlnx)

lny=lnx(ln(lnx))

Let y=lnu and u=lnx.

dydx=1u×1x=1lnx×1x=1xlnx

1y(dydx)=1x×ln(lnx)+lnxxlnx

1y(dydx)=ln(lnx)x+1x

dydx=y×ln(lnx)+1x

dydx=(lnx)lnx(ln(lnx)+1)x

The second derivative can be found using the product rule to differentiate the upper term and the quotient rule to differentiate the entire expression.

You can do the algebra.

Hopefully this helps!