百威英博官网:X^10+X^5+1=?

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因式分解

x^10+x^5+1
=(x-1)(x^10+x^5+1)/(x-1)
=(x^11-x^10+x^6-x^5+x-1)/(x-1)
其中x^11-x^10+x^6-x^5+x-1
=(x^11-x^5)-(x^10-x)+(x^6-1)
=(x^6-1)(x^5+1)-x(x^9-1)
=(x^3-1)(x^3+1)(x^5+1)-x(x^3-1)(x^6+x^3+1)
=(x^3-1)[(x^8+x^5+x^3+1)-(x^7+x^4+x)]
=(x^3-1)(x^8-x^7+x^5-x^4+x^3-x+1)
∴原式=(x^3-1)(x^8-x^7+x^5-x^4+x^3-x+1)/(x-1)
=(x^2+x+1)(x^8-x^7+x^5-x^4+x^3-x+1)

X^10+X^5+1=X^10+X^5+1+X^5-X^5
=(X^5+1)^2-X^5
=(X^5+1-X^2/5)(X^5+1+X^2/5)