- #1

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## Homework Statement

Is there like a formula with a name easy to remember of which the following is a specific instance:

x^200 -y^200 = (x-y)(x^199+x^198y+... + y^198*x + y^199)

?

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- Thread starter ehrenfest
- Start date

- #1

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Is there like a formula with a name easy to remember of which the following is a specific instance:

x^200 -y^200 = (x-y)(x^199+x^198y+... + y^198*x + y^199)

?

- #2

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Not that I've ever heard...

[tex](x+y)(x-y)(x^2+y^2)(x^4+y^4)(x^4+x^3y+x^{2}y^2+xy^3+y^4)(x^4-x^3y+x^2y^2-xy^3+y^4)(x^8-x^6y^2+x^4y^4-x^2y^6+y^8)(x^{16}-x^{12}y^4+x^8y^8-x^4y^{12}+y^{16})[/tex]

[tex](x^{20}+x^{15}y^5+x^{10}y^{10}+x^5y^{15}+y^{20})(x^{20}-x^{15}y^5+x^{10}y^{10}-x^5y^{15}+y^{20})(x^{40}-x^{30}y^{10}+x^{20}y^{20}-x^{10}y^{30}+y^{40})[/tex]

[tex](x^{80}-x^{60}y^{20}+x^{40}y^{40}-x^{20}y^{60}+y^{80})[/tex]

Sorry wouldn't fint onto one line...

Maybe to can find a pattern to that mess though. If not, well, it took my calculator about 3 second to find the answer, might want to use one the next time you need to factor that...

[tex](x+y)(x-y)(x^2+y^2)(x^4+y^4)(x^4+x^3y+x^{2}y^2+xy^3+y^4)(x^4-x^3y+x^2y^2-xy^3+y^4)(x^8-x^6y^2+x^4y^4-x^2y^6+y^8)(x^{16}-x^{12}y^4+x^8y^8-x^4y^{12}+y^{16})[/tex]

[tex](x^{20}+x^{15}y^5+x^{10}y^{10}+x^5y^{15}+y^{20})(x^{20}-x^{15}y^5+x^{10}y^{10}-x^5y^{15}+y^{20})(x^{40}-x^{30}y^{10}+x^{20}y^{20}-x^{10}y^{30}+y^{40})[/tex]

[tex](x^{80}-x^{60}y^{20}+x^{40}y^{40}-x^{20}y^{60}+y^{80})[/tex]

Sorry wouldn't fint onto one line...

Maybe to can find a pattern to that mess though. If not, well, it took my calculator about 3 second to find the answer, might want to use one the next time you need to factor that...

Last edited:

- #3

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which calculator do you have? i been thinking about upgrading to a TI-89 ...

- #4

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which calculator do you have? i been thinking about upgrading to a TI-89 ...

Ti-89 Titanium

- #5

HallsofIvy

Science Advisor

Homework Helper

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## Homework Statement

Is there like a formula with a name easy to remember of which the following is a specific instance:

x^200 -y^200 = (x-y)(x^199+x^198y+... + y^198*x + y^199)

?

Do you mean

[tex]x^n- y^n= (x-y)(x^{n-1}+ x^(n-2)y+ /cdot/cdot/cdot+ xy^{n-2}+ y^{n-1}[/tex]?

I've never worried about it having a name!

- #6

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Do you mean

[tex]x^n- y^n= (x-y)(x^{n-1}+ x^(n-2)y+ /cdot/cdot/cdot+ xy^{n-2}+ y^{n-1}[/tex]?

I've never worried about it having a name!

Yes. I just forget identities so easily when I have to remember them by their statement not some label. However, you're right, this is a pretty simple one that is easily verifiable and probably doesn't warrant a name!

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