`y = x ln(x)` Locate any relative extrema and points of inflection.

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embizze eNotes educator| Certified Educator

We are asked to locate any relative extrema or inflection points for the graph of `y=xlnx ` :

The domain of the function is x>0.

Extrema can only occur at critical points; that is when the first derivative is zero or fails to exist.

`y'=lnx+x*1/x ==> y'=lnx + 1 `

This function is continuous and differentiable for all x in the domain, so setting y'=0 we get:

`lnx+1=0 ==> lnx=-1 ==> x=1/e~~0.368 `

For 0<x<1/e the first derivative is negative and for x>1/e it is positive, so the only extrema is a minimum at x=1/e.

Inflection points can only occur when the second derivative is zero:

`y''=1/x>0 forall x ` so there are no inflection points.

The graph: