Question 1155272
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In your list, you missed -1, 10 and - 10.


Notice, that in your problem, the leading coefficient is 1 (one, ONE), and it makes the solution much EASIER.


The better way is to present your list in this form


    +/-1, +/-2, +/-4, +/-5, +/-10, +/-20.


When you present in this form, you are (almost) guaranteed from missing the terms.
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&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;<U>Notices and guidelines</U>


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    In this problem, the leading coefficient is 1 (at x^3).

    The constant term is 20.

    You must list all the numbers  +/- {{{factors_of_the_constant_term/factors_of_the_leading_coefficient}}}.
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IGNORE &nbsp;THE &nbsp;POST &nbsp;BY &nbsp;@MathLover1, &nbsp;since she presented &nbsp;TOTALLY &nbsp;WRONG &nbsp;solution.


Ignore it for your safety (!) (!) (!)



Dear @MathLover1, &nbsp;in my view, &nbsp;it is &nbsp;ABSOLUTELY &nbsp;INAPPROPRIATE &nbsp;for a tutor to consult students/visitors 
in a level as you did it in this case &nbsp;(and in many other cases I observed).


I know that you are able to consult satisfactory/successfully on many simple level problems.


Do it in those areas/topics, &nbsp;where you are confident, &nbsp;and do not go outside, &nbsp;where you have no enough knowledge/expertise.


One more advise: &nbsp;<U>CHECK</U> &nbsp;yourself, &nbsp;using both the formal checks and the common sense.