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We have never done finding the roots of a cubic equation before and I cannot figure it out from looking on the internet, the formulas are all horrible to understand.

Any help would be appreciated.

James

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- Thread starter James...
- Start date

- #1

- 25

- 0

We have never done finding the roots of a cubic equation before and I cannot figure it out from looking on the internet, the formulas are all horrible to understand.

Any help would be appreciated.

James

- #2

symbolipoint

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Your wish for knowing "formulas which are horrible to understand" reflects ones first-through study of College Algebra, in which you learn to deal with Descartes Law of Signs, Rational Roots Theorem, the Factor and Remainder Theorems. You could spend a good 2 months studying this stuff from a College Algebra textbook and become very well knowledgable about these things. You really want to KNOW this stuff and you are not really concerned with a course grade for credit. Those laws and theorems really CAN be well learned if you spend the time seriously studying them; keeping the knowledge several weeks later is another thing entirely.

- #3

symbolipoint

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Actually for just a cubic equation, you don't need those fancy formulas. Usually, you would be expected to factor into linear and possibly a quadratic factor and determine what values of the variable make the product equal to zero.

- #4

symbolipoint

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You could resort to Rational Roots Theorem and polynomial division, but not much else would be needed. Do you need an example?

- #5

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I managed to get the answer by creating a linear and quadratic factor of the cubic equation. We have done this before many times, but never as part of a polynomial, I should have realised I could have done it as it equals zero and therfore I can split it into factors.

I will have a play about with the Rational Roots theorum and polynomial division tomorrow but I may need an example depending on how i find it.

Thanks again

James

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