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06-17-2020
09:58 AM

06-17-2020
09:58 AM

Hi,

Distractedly, I used the "solve" operator to solve the given polynomial equation. It gives a solution but the answer is not complete. Why solve does not give the correct answer?

Solved! Go to Solution.

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06-17-2020
10:45 AM

06-17-2020
10:45 AM

It's correct use, but potentially incorrect results, of *solve*.

Apparently the exponent 1/3 is problematic. When given "(2*x+1)^(1/3)-(x^3-1)/2, solve x",

this is what WolframAlpha makes of it:

Note that:

and

each give you all 9 roots, but:

Gives 7 roots, and 6 duplicates. maybe if you add ", all" to the solve command it comes up with more.

Finally, check if -1 is a solution:

Apparently not. This is the wonder world of the exponent function when it's argument is (potentially) complex.

Success!

Luc

2 REPLIES 2

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06-17-2020
10:45 AM

06-17-2020
10:45 AM

It's correct use, but potentially incorrect results, of *solve*.

Apparently the exponent 1/3 is problematic. When given "(2*x+1)^(1/3)-(x^3-1)/2, solve x",

this is what WolframAlpha makes of it:

Note that:

and

each give you all 9 roots, but:

Gives 7 roots, and 6 duplicates. maybe if you add ", all" to the solve command it comes up with more.

Finally, check if -1 is a solution:

Apparently not. This is the wonder world of the exponent function when it's argument is (potentially) complex.

Success!

Luc

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06-17-2020
01:11 PM

06-17-2020
01:11 PM

Re: Incorrect use of solve

Thanks for the reply. Greetings.