quadratic equation: how to solve x^3 -15x + 15  TOPIC_SOLVED

Quadratic equations and inequalities, variation equations, function notation, systems of equations, etc.

quadratic equation: how to solve x^3 -15x + 15

Postby Motherof8 on Sun Mar 18, 2012 4:10 pm

How would you solve this equation? x^3 -15x + 15. When I say (x^2 -15) (x -1) I end up with an extra -x ^2.
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Re: quadratic equation: how to solve x^3 -15x + 15  TOPIC_SOLVED

Postby nona.m.nona on Sun Mar 18, 2012 11:32 pm

Motherof8 wrote:How would you solve this equation? x^3 -15x + 15.

Since the degree of the leading term is 3, this is therefore a cubic, and not a quadratic, expression.

To solve (by which I assume you mean finding the zeroes), one would customarily use the methodology outlined in this article. However, that methodology will fail due to the fact that this expression has no rational zeroes. Therefore, one would need to use numerical methods to approximate the zeroes.
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