Excel's Formula - sisman

470
Part V: Miscellaneous Formula Techniques
The following formula, in cell G3, calculates the value for c:
=EXP(G2)
Column C shows the predicted y values for each value of x, using the calculated values for b and
c. For example, the formula in cell C2 is as follows:
=$G$3*EXP($F$2*A2)
Column D uses the GROWTH function in an array formula to generate predicted y values. The
array formula, entered in D2:D11, appears like this:
{=GROWTH(B2:B11,A2:A11)}
Polynomial trendline
When you request a polynomial trendline, you also need to specify the order of the polynomial
(ranging from 2 through 6). The equation for a polynomial trendline depends on the order. The
following equation, for example, is for a third-order polynomial trendline:
y = (c3 * x^3) + (c2 * x^2) + (c1 * x^1) + b
Notice that there are three c coefficients (one for each order).
Figure 17-30 shows a chart with a third-order polynomial trendline added. A four-element array
formula entered in F2:I2 calculates the values for each of three c coefficients and the b coefficient.
The formula is
{=LINEST(B2:B11,A2:A11^{1,2,3})}