The third root of a number

This is a discussion on The third root of a number within the C Programming forums, part of the General Programming Boards category; I was wondering how to calculate the third square root of a number. Or the nth square root of a ...

  1. #1
    Frequently Quite Prolix dwks's Avatar
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    The third root of a number

    I was wondering how to calculate the third square root of a number. Or the nth square root of a number. Is there a function for it?

    I know you can calculate the fourth square root like this:
    Code:
    #include <math.h>
    
    sqrt(sqrt(81));
    But that only works for multiples of two.
    dwk

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  2. #2
    Just Lurking Dave_Sinkula's Avatar
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    I don't know if I understand what you mean by "third" and "fourth" square root. If you just mean the third root, 4th root, nth root, then I'd say use pow.
    Code:
    pow(x, 1.0 / n);
    7. It is easier to write an incorrect program than understand a correct one.
    40. There are two ways to write error-free programs; only the third one works.*

  3. #3
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    he means, the cubed root, (when he talking about third)

    8 * 8 * 8 = 512 // he want to know how to find the 8

    3 * 3 * 3 = 27 // he want to know how to find the 3


    or if this came up


    5 * 5 * 5 * 5 = 625 // he want to know how to find the 5

  4. #4
    Registered User Tonto's Avatar
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    Of course he does. And of course, square roots, cube roots, etc. are really just fractional exponents. Thus:

    Code:
    #include <math.h>
    #include <stdio.h>
    
    int main ()
    {
    	printf("%2.2f", pow(125, 1.0 / 3.0));
    	return 0;
    }
    Retuns a clean 5.

  5. #5
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    An alternative, which has both advantages and disadvantages over using pow(), is

    Code:
    #include <math.h>
    #include <stdio.h>
    
    int main ()
    {
           double x = 125.0;
           int n;
    	printf("%2.2f", exp(log(x)/n));   /* x an n must both be positive */
    	return 0;
    }

  6. #6
    Frequently Quite Prolix dwks's Avatar
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    Okay, thanks. I don't know why I never thought of the pow() version . . . .
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
    "The only real mistake is the one from which we learn nothing." -- John Powell


    Other boards: DaniWeb, TPS
    Unofficial Wiki FAQ: cpwiki.sf.net

    My website: http://dwks.theprogrammingsite.com/
    Projects: codeform, xuni, atlantis, nort, etc.

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