polynomial help (1 Viewer)

AfroNerd · Feb 23, 2016

i wasn't quite sure how to find m

Two roots of x^3 +mx^2+15x-7=0 are equal and rational. find m.

HeroicPandas · Feb 23, 2016

Do you know a relationship between a polynomial's roots and it's coefficients?

BLIT2014 · Feb 23, 2016

Drsoccerball · Feb 23, 2016

AfroNerd said:
i wasn't quite sure how to find m

Two roots of x^3 +mx^2+15x-7=0 are equal and rational. find m.

$$ If two of the roots are equal without the information of them being rational one way you could do it is :$

$\alpha ^3 +m \alpha ^2 +15 \alpha -7 = 0 ---(1)$

$3 \alpha ^2 +2m \alpha +15=0---(2) $ Since it has a double root $$

$(2) \cdot \frac{\alpha}{2} ---(3)$

$(2)=(3) $ Solve for alpha then sub back into any equation. $$

BLIT2014 · Feb 23, 2016

http://community.boredofstudies.org/13/mathematics-extension-1/345490/polynomials-roots.html

AfroNerd · Feb 23, 2016

where did u get a^2 + 14/a = 15 from

leehuan · Feb 23, 2016

AfroNerd said:
where did u get a^2 + 14/a = 15 from

By substituting his second equation into the first?

Just use InteGrand's comment that he linked though.

polynomial help (1 Viewer)

AfroNerd

New Member

HeroicPandas

Heroic!

BLIT2014

The pessimistic optimist.

Drsoccerball

Well-Known Member

BLIT2014

The pessimistic optimist.

AfroNerd

New Member

leehuan

Well-Known Member

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