若(x-1)(y+1)=3,xy(x-y)=4,求x的7次方减去y的7次方的值。

2024-12-29 04:59:44
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回答1:

(x-1)(y+1)=xy+x-y-1=3,xy+(x-y)=4,xy(x-y)=4,xy=2,x-y=2,x²+y²=8,x³-y³=(x-y)(x²+xy+y²)=20,(x²+y²)(x³-y³)=160,x^5+x³y²-x²y³-y^5=x^5+x²y²(x-y)-y^5=x^5+8-y^5=160,x^5-y^5=152,(x²+y²)(x^5-y^5)=1216,x^7-y^7+x^5y²-x²y^5=x^7-y^7+x²y²(x³-y³)=x^7-y^7+80=1216,x^7-y^7=1136。