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Incorrect use of solve

SOLVED
-MFra-
Topaz I

Incorrect use of solve

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?solve e poly.jpg

1 ACCEPTED SOLUTION

Accepted Solutions

Re: Incorrect use of solve

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:

LucMeekes_0-1592404767725.png

Note that:

LucMeekes_1-1592404858021.png

and

LucMeekes_2-1592404881988.png

LucMeekes_3-1592404901548.png

each give you all 9 roots, but:

LucMeekes_4-1592404927925.png

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:

LucMeekes_0-1592406119282.png

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

 

Success!

Luc

 

View solution in original post

2 REPLIES 2

Re: Incorrect use of solve

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:

LucMeekes_0-1592404767725.png

Note that:

LucMeekes_1-1592404858021.png

and

LucMeekes_2-1592404881988.png

LucMeekes_3-1592404901548.png

each give you all 9 roots, but:

LucMeekes_4-1592404927925.png

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:

LucMeekes_0-1592406119282.png

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

 

Success!

Luc

 

View solution in original post

Re: Incorrect use of solve

Thanks for the reply. Greetings.

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