# [Community Puzzle] Derivative time ! - part1

Coding Games and Programming Challenges to Code Better

Created by @pluieciel,validated by @Myrrhe,@Sceurpien and @BleedingWithin.
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I’ve forgotten all calculus stuff. Could someone tell me what is the difference between two versions of a test case?
Test case “power with number”

((x^2)+(9*(x+y)))
x
x 1 y 2

== vs ==

((x^2)+(9*(x+y)))
x y
x 1 y 2

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In the first case, you derive once (with x), in the second case, you derive with x, then with y.

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After derive with x, will the result be
2x + 9 + 9y

and then derive with y, will the result be
2x + 9

?

starting from:

x^2 + 9x + 9y

d/dx gives 2x + 9 because 9y is considered a constant number for x.

Then d/dy gives 0.

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That makes sense. Thank you.

Hi there,
I am quite stuck ont his problem. My approach is to convert the string function to a executable function, where I can evaluate it at every point. And then I apply the definition of derivation: lim(h to 0) of (f(x+h)-f(x))/h for each derivate. Up to de second derivative, eveything runs smoothly. Third derivatives dont work at all. Any one has followed this approach? Any thoughts? Any other approaches to explore?