已知x^2-3x+1=0,求x^3+1⼀x^3

2024-12-16 13:39:34
推荐回答(2个)
回答1:

x^2-3x+1=0
x^2+1=3x
x+1/x=3
x^3+1/x^3=(x+1/x)(x^2-1+1/x^2)=(x+1/x)[(x+1/x)²-3]=3×(3²-1)=24

回答2:

x^2-3x+1=0,x-3+1/x=0 (因为x不等于0,两边同时除以x)
x+1/x=3
(x+1/x)^2=9
x^2+1/x^2+2=9
x^2+1/x^2=7

x^3+1/x^3=(x+1/x)(x^2+1/x^2-1)=3*(7-1)=18打酱油