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5-Regular Member
Mar 16, 2026 10:34 AM UTC
Question

Problem with basic calculations

mathcad cannot handle correctly the swap of negative symbol in odd powers.
Specific, calculating this expression (-1/8)^(-2/3) gives an imaginary result instead of the 4 as result

    8 replies

    terryhendicott
    21-Topaz II
    Mar 16, 2026 11:26 AM UTC

    Prime gets this:

    Capture.JPG

    Maple Flow gets this:

    Capture2.JPG

    Matlab gets this:

    Capture3.JPG

    Julia:

    Capture4.jpg

    Cheers

    Terry

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    terryhendicott
    21-Topaz II
    Mar 16, 2026 12:14 PM UTC

     

    Octave:

    Capture5.JPG

    Wolfram:

    Capture6.JPG

    Python:

    Capture7.JPG

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    5-Regular Member
    Mar 16, 2026 3:29 PM UTC

    The original solution as presented in the book MODERN ENGINEERING MATHEMATICS
    Glyn James, Phil **bleep**, Sixth Edition

    page 7

    is as shown in screenshot. Its just a simple and direct solution on this.

     

    Screenshot 2026-03-16 152720.png

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    terryhendicott
    21-Topaz II
    Mar 16, 2026 6:26 PM UTC

    Hi,

    Both answers are correct:

    Capture8.JPG

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    terryhendicott
    21-Topaz II
    Mar 17, 2026 7:22 AM UTC

    Thanks for spotting this, remember 7 mathematical programs get the complex result.

    You can with some manipulation of the problem get 4.

    The first step in the solution from the book gets 4.

    Capture.JPG

    It seems cube root gets 4 raising to the 1/3 power gets the complex result.

    Capture2.JPG

    Very interesting learning thank you for spotting this.

    Cheers

    Terry

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