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GuessWho
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#1
Report Thread starter 15 years ago
#1
hi, can anyon help me on the following things:

im trying to find and explain the different stages of the formula for pentagonal numbers, the numbers are:
1, 6, 16, 31, 51, 76

So the difference between them is 5 10 15 20 25

So the 2nd difference is 5 5 5 5

as a sarter i know that the first half of the formual is 2.5n2, but now im stuck, so can anyone tell me how to get the rest of the formula, by explaining each stage in the process??

Thanks

P.S
can you tell me the same eplanations and process for getting the formulas of hexagonal, heptagonal, octagonal, nonagonal (9 sides), decagonal
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Valen
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#2
Report 15 years ago
#2
Write out the first half of the formula as its own series. Subtract that from your original series. Repeat original procedure (method of differences) on this new series.
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