shirle88
幼苗
共回答了16个问题采纳率:81.3% 举报
(x-1)(y+1)=3
即xy+(x-y)=4
又xy(x-y)=4
则xy,(x-y)是方程z^2-4x+4=0的解,
xy=2,x-y=2
(x+y)^2=(x-y)^2+4xy=12
x+y=2√3或x+y=-2√3
x=√3+1,y=√3-1
或x=1-√3,y=-1-√3
x^7-y^7自己带入吧!
1年前
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10
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shirle88
xy=2,x-y=2 (x-y)^2=4 x^2-2xy+y^2=4 x^2+y^2=8 X^3-Y^3=(x-y)(x^2+xy+y^2)=2*(8+2)=20 (X^3-Y^3)( X^2+Y^2)=20*8 X^5+X^3Y^2-Y^3X^2-Y^5=160 X^5+X^2Y^2(X-Y)-Y^5=160 X^5-Y^5=160-4*2=152 (X^5-Y^5)(X^2+Y^2)=152*8 X^7+X^5Y^2-Y^5X^2-Y^7=1216 X^7-Y^7=1216-X^2Y^2(X^3-Y^3) =1216-4*20=1136