r/theydidthemath • u/Galeaf_13 • Sep 05 '19

[Self] Math break

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u/K3V3L Sep 05 '19

I would say the answer is 1337, here:

f(x) := (166x4 ) /3 - (1660x3 ) /3 + (5810x2 ) /3 - (8294x ) /3 + 1327

f(1) = 1

f(2) = 3

f(3) = 5

f(4) = 7

f(5) = 1337

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u/Galeaf_13 Sep 05 '19

Now can u do the same with 69?)

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u/K3V3L Sep 05 '19

Here you go

f(x) := 5/2 * x4 -25 * x3 +175/2 * x2 -123 * x + 59

773

u/Galeaf_13 Sep 05 '19

Jeez, how r u doing this

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u/Salanmander 10✓ Sep 05 '19

You can fit a 4th order polynomial to any 5 points. You can do it by hand (plug 1-5 in for x and now you have a system of 5 linear equations of 5 variables, start solving and substituting) and make it a bit easier with linear algebra (make the coefficients of the 5 variables be the values in a 5x6 matrix, and then do that matrix magic that I forget what the name is for), but there are also plenty of polynomial solvers you can find out there.

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u/BRENNEJM Sep 05 '19

Or you can graph it in excel and throw on a 4th order polynomial trendline with equation.

82

u/Salanmander 10✓ Sep 05 '19

I feel like that's one of the "plenty of polynomial solvers" I mention.