Page 434 - Excel for Scientists and Engineers: Numerical Methods

APPENDIX 4 EOUATIONS FOR CURVE FITTING 41 1

y = aebx (A4-3)
The sign of b is often negative (as in radioactive decay), giving rise to the
decreasing behavior shown in Figure A4-2.
The linearized form of the equation is In y = bx + In a; the Trendline type is
Exponential.

Exponential Growth. If the sign of b in equation A4-3 is positive, the
curvature is upwards, as in Figure A4-3.

r,

0 2 4 6 8 10
X
Figure A4-3. Exponential increase.
The curve follows equation A4-3 with a = 0.1 and b = 0.5.
The Trendline equation is shown on the chart.

Exponential Decrease or Increase Between Limits. If the curve
decreases exponentially to a nonzero limit, or rises exponentially to a limiting
value as in Figure A4-4, the form of the equation is
y = aebx + c (A4-4)
Excel's Trendline cannot handle data of this type.