Page 205 - Excel for Scientists and Engineers: Numerical Methods

182 EXCEL: NUMERICAL METHODS

=goalseek(B5,A5,ElO)

Note that the GoalSeek function does not modify the value of the changing
cell (in this example cell A5) nor does it result in a change in the cell containing
the function (in this example cell 85). These values are merely copied and used
as inputs for the VBA code. The final value of the changing cell is returned by
the GoalSeek function (in this example in cell D14). As a check, the target cell
formula was entered in cell El4 so as to calculate F(x) using the value of x
returned by Goalseek.
Some functions have more than one value of x that can satisfy the
relationship F(x) = objective-value; in these cases the user must use the optional
argument initial_va/ue to control the value of x that is returned.

Figure 8-41. Using the GoalSeek custom function to find the value ofx
that makes the function y = x2 + 6x - 10 have a specified value (here, y = 2 10).
(folder 'Chapter 08 Examples', workbook 'Goalseek Fn', sheet 'Intersection of line with h (2)')
If you change the values of aa, bb, cc, or H, the function value will update to
find the new intersection value. In contrast, if you use the Goal Seek.. . tool, you