Find when 2x^3+x-5 is equal to zero

  • #1
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I need to find when 2x^3+x-5 is equal to zero and I'm stuck

2x^3+x-5=0
5=2x^3+x....then what?
 

Answers and Replies

  • #2
Hurkyl
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You sure you have the right problem?


There is a really nice theorem for finding all of the rational zeroes of a polynomial that involves the first and last terms of the polynomial, have you seen it yet?
 
  • #3
HallsofIvy
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Hurkyls method show that there are no rational solutions. That means that this cannot be factored with integer coefficients. There is a "cubic formula" but it is very messy. It is probably best solved numerically.

(The method I used was to graph it on my calculator, then "zoom" in on the x-intercept!)
 

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