Answer
(a) The natural logarithm is the logarithm with the base equal to Euler's number $e$:
(b) The common logarithm is the logarithm with the base equal to $10$.
(c) The graphs are shown on the figure below (exponential is blue and the logarithm is red). The line $y=x$ is dashed.
Work Step by Step
(a) The natural logarithm is the logarithm with the base equal to Euler's number $e$:
$$\ln x =\log_{e}x.$$
(b) The common logarithm is the logarithm with the base equal to $10$:
$$\log x= \log_{10}x$$
(c) The graph of the natural logarithm is obtained by reflecting the natural exponential function abour $y=x$ line and they are shown on the figure below (exponential is blue and the logarithm is red). The line $y=x$ is dashed.
