Excel's Formula - sisman

460
Part V: Miscellaneous Formula Techniques
Creating awesome designs
Figure 17-21 shows an example of an XY chart that displays hypocycloid curves using random values.
This type of curve is the same as that generated by Hasbro’s popular Spirograph toy, which
you may remember from childhood.
Figure 17-21: A hypocycloid curve.
The companion CD-ROM contains two hypocycloid workbooks: the simple example
shown in Figure 17-21 (named hypocycloid chart.xlsx), and a much more complex
example (named hypocycloid animated.xlsm) that adds animation and a few other
accoutrements. The animated version uses VBA macros.
The chart uses data in columns D and E (the x and y ranges). These columns contain formulas
that rely on data in columns A through C. The formulas in columns A through C rely on the values
stored in E1:E3. The data column for the x values (column D) consists of the following formula:
=(A6–B6)*COS(C6)+B6*COS((A6/B6–1)*C6)
The formula for the y values (column E) is as follows:
=(A6–B6)*SIN(C6)–B6*SIN((A6/B6–1)*C6)