You may have recognized that the general shape of the graph matches the graph of a logarithm. To see that it is not an exact match, you need to use a calculator. For example, $\displaystyle{f{{\left({10}\right)}}}={\log{{2.5}}}\approx{0.4}\usepackage{cmbright}\Huge\$ . However, for the given graph, when $\displaystyle{x}={10}\usepackage{cmbright}\Huge\$ , y is very close to 1.