You may have recognized that the general shape of the graph matches the graph of a logarithm. By knowing that $\displaystyle{\log{{10}}}={1}\usepackage{cmbright}\Huge\$ you can check without using a calculator a point on the graph. If $\displaystyle{f{{\left({x}\right)}}}={\log{{x}}}\usepackage{cmbright}\Huge\$ then $\displaystyle{f{{\left({10}\right)}}}={\log{{10}}}={1}\usepackage{cmbright}\Huge\$ . However, on this graph when $\displaystyle{x}={10}\usepackage{cmbright}\Huge\$ , y is close to 2.3 not 1, so this is not a graph of $\displaystyle{f{{\left({x}\right)}}}={\log{{x}}}\usepackage{cmbright}\Huge\$ . Other points can be checked with a calculator.