..已知X2-3X=1=0,求X3+1/X3的值

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..已知X2-3X=1=0,求X3+1/X3的值
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..已知X2-3X=1=0,求X3+1/X3的值
..已知X2-3X=1=0,求X3+1/X3的值

..已知X2-3X=1=0,求X3+1/X3的值
x^2-3x+1=0 x=0不是方程的根
两边同除以x 有x+1/x=3
x^2+1/x^2=(x+1/x)^2-2=7
所以
x³+1/x³=(x+1/x)(x²-1+1/x²)
=3×(7-1)
=18

x²-3x+1=0 是这样的吧
x²+1=3x
x+1/x=3
x³+1/x³
=(x+1/x)(x²+1/x²-1)
=(x+1/x)[(x+1/x)²-3]
=3(3²-3)
=3×6
=18

看不清啊 亲!!!