x+y=xy=3

find x^3 + y^3

Anyone? Could really use some help on this the extra credit would be nice to have.

The work is more important than the answer, so any idea on how to get started so i could begin figuring it would be much appreciated.

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- Dec 8th 2008, 11:43 PMTwertzalgebra equations
x+y=xy=3

find x^3 + y^3

Anyone? Could really use some help on this the extra credit would be nice to have.

The work is more important than the answer, so any idea on how to get started so i could begin figuring it would be much appreciated. - Dec 8th 2008, 11:57 PMChop Suey
- Dec 9th 2008, 12:05 AMTwertz
ok i'm still stuck. it's Find x^3 + y^3 so am i trying to cube the original equation? a bit more of a boost maybe?

i've got to be taking it in the wrong direction

i cubed the original equation and moved everything so it was x^3 + y^3= -3x^2y-3xy^2-x^3y^3-27 - Dec 9th 2008, 12:20 AMChop Suey
- Dec 9th 2008, 12:24 AMnzmathman
You have $\displaystyle x + y = 3$

So $\displaystyle (x + y)^3 = 27$

$\displaystyle (x + y)^3 = x^3 + 3x^2y + 3xy^2 + y^3$

$\displaystyle 27 = x^3 + 3x^2y + 3xy^2 + y^3$

$\displaystyle x^3 + y^3 = 27 - 3x^2y - 3xy^2 $

$\displaystyle x^3 + y^3 = 27 - 3xy(x + y) $

$\displaystyle x^3 + y^3 = 27 - 3 \times 3 \times 3 \quad$ (since x+y = 3 and xy = 3 - Dec 9th 2008, 01:06 AMmr fantastic
- Dec 9th 2008, 02:24 AMCaptainBlack