Techniques of Differentiation - Derivatives of Natural Logarithmic Functions

Techniques of Differentiation - Derivatives of Natural Logarithmic Functions

Secondary 4

The function \(\mathrm{f}\) is given by \(\mathrm{f}(x) = \frac{\ln 2x}{x}\), \(x > 0\).

    1. Show that \(\mathrm{f}'(x) = \frac{1 - \ln 2x}{x^2}\).
    2. Show that the graph of \(\mathrm{f}\) can have only one local maximum or minimum point.
    3. Find the coordinates of the maximum point on the graph of \(\mathrm{f}\).
  1. By showing that the second derivative \(\mathrm{f}''(x) = \frac{2 \ln 2x - 3}{x^3}\) or otherwise, find the \(x\)-coordinates of the point of inflexion on the graph of \(\mathrm{f}\).
Answer:(a)(iii) \(\left( \frac{\operatorname{e}}{2},\frac{2}{e} \right)\) (b) \(x=\frac{{{\operatorname{e}}^{1.5}}}{2}\)

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