Spreadsheets: Excel and LibreOffice Calc: the sum of a geometric series
The tutor shows the seriessum() function, found on both Excel and LibreOffice Calc.
A geometric series has the form
Sn = cr0 + cr1 + … + crn-1
An example is
3 + 3*4 + 3*42 + … + 3*45
which might also be written
3 + 12 + 48 + 192 + 768 + 3072
With Excel or LibreOffice Calc, the function to evaluate that sum is =seriessum(a,b,c,d), where
- a is the number whose exponent increases each term (4, in the example just above)
- b is the initial exponent of a (0, in the example just above)
- c is the increment by which the exponent increases each term (1, in the example just above)
- d is an array of the coefficients of the terms. In the example just above, the coefficient is always 3. You’d need to enter {3,3,3,3,3,3} for d: one 3 for each term.
So, to evaluate 3 + 12 + 48 + 192 + 768 + 3072, you might enter
=seriessum(4,0,1,{3,3,3,3,3,3})
Hopefully you receive the answer 4095:)
Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.
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