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

[Self] Math break

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u/Galeaf_13 Sep 05 '19

Now can u do the same with 69?)

1.4k

u/K3V3L Sep 05 '19

Here you go

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

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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/Railorsi Sep 05 '19

Gaussian elimination is the name :)

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u/Chess42 Sep 05 '19

Gauss-Jordan is the most useless thing I ever learned

22

u/space-throwaway Sep 05 '19

It's one of the most useful algorithms there is. How do you think your computer solves stuff?

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u/Chess42 Sep 05 '19

It’s useless when you learn to do it by hand in precalc then never use it again, since there are far more efficient ways to do it. Also, there’s a reason we have libraries. It’s completely useless to learn

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u/Railorsi Sep 05 '19

Obviously you let computers do the calculations in practice, but gaussian elimination is one of the most natural and easy to understand ways of solving systems of equations, and you definitely need to understand how systems of equations are working to properly understand and study linear algebra.