Graph log(x) and ln(x) on the same diagram for −1 < x < 2. From the graphs summarise the properties of the log functions. How does the size of the base affect the shape of the graph?
Calculate a table of values for each function, using your calculator to evaluate the logs or, better still, use Excel. No real value exists for the logs of zero (doesn’t exist) or logs of negative numbers (complex). This is indicated on the calculator by – E – and in Excel by #NUM!. Table 4.15 outlines the points used to plot the graphs in Figure 4.20. From Figure 4.20, some properties of log functions can be deduced:
In addition, the graph of loge(x) is steeper, that is, it increases and decreases more rapidly than log10(x).
Table 4.15 Values of log(x) and ln(x) | ||
x | log(x) | ln(x) |
−0.2 | #NUM! | #NUM! |
0 | #NUM! | #NUM! |
0.2 | −0.7 | −1.61 |
0.4 | −0.4 | −0.92 |
0.6 | −0.22 | −0.51 |
0.8 | −0.1 | −0.22 |
1 | 0 | 0 |
1.2 | 0.08 | 0.18 |
1.4 | 0.15 | 0.34 |
1.6 | 0.20 | 0.47 |
1.8 | 0.26 | 0.59 |