Microsoft Office Tutorials and References
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Polynomial trendline
Figure 5-13: A chart displaying an exponential trendline
Polynomial trendline
A polynomial trendline defines a curved line and describes data that fluctuates in
an orderly pattern. 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 of the polynomial.
SECOND-ORDER TRENDLINE
A second-order trendline (also known as a quadratic trendline) describes data that
resembles a U or an inverted U. Following is the equation for a second-order
polynomial trendline:
y = (c2 * x^2) + (c1 * x^1) + b
Notice that there are two c coefficients (one for each order).
Figure 5-14 shows a chart with a second-order polynomial trendline added.
Formulas entered in E2:G2 calculate the values for each of the c coefficients and
the b constant. The formulas are as follows:
E2:
=INDEX(LINEST(B2:B11,A2:A11^{1,2}),1)
F2:
=INDEX(LINEST(B2:B11,A2:A11^{1,2}),1,2)
G2:
=INDEX(LINEST(B2:B11,A2:A11^{1,2}),1, 3)
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