（1）若x+1/x=3，求x^2/(x^4+x^2+1)的值. （2）若1/x-1/y=2，求(4
（1）若x+1/x=3，求x^2/(x^4+x^2+1)的值.
（2）若1/x-1/y=2，求(4x+5xy-4y)/(x-3xy-y)的值.
第1个回答 2019-01-17
第2个回答 2019-01-17
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第3个回答 2019-01-17
(1)
x+1/x=3
x^2+1/x^2 +2 =9
x^2+1/x^2 =7
x^2/(x^4+x^2+1)
=1/( x^2 +1 +1/x^2)
=1/(7+1)
=1/8
（2）
1/x-1/y=2
y-x =2xy
x-y =-2xy
(4x+5xy-4y)/(x-3xy-y)
=[ 4(x-y)+5xy] /[ (x-y) -3xy]
=(-8+5).( -2 -3)
=3/5
x+1/x=3
x^2+1/x^2 +2 =9
x^2+1/x^2 =7
x^2/(x^4+x^2+1)
=1/( x^2 +1 +1/x^2)
=1/(7+1)
=1/8
（2）
1/x-1/y=2
y-x =2xy
x-y =-2xy
(4x+5xy-4y)/(x-3xy-y)
=[ 4(x-y)+5xy] /[ (x-y) -3xy]
=(-8+5).( -2 -3)
=3/5
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