已知x=4-根号7⼀3.求x^2⼀x^4+x^2+1

2025-05-11 22:20:58
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回答(1):

(x^4+x^2+1)/x^2=x^2+1+1/x^2

x^2=(4-根号7/3)^2=(16+7-8根号7)/9=(23-8根号7)/9

1/x^2=(1/x)^2=[1/(4-根号7/3)]^2=[3/(4-根号7)]^2=[3(4+根号7)/(4-根号7)(4+根号7) ]^2=[(4+根号7)/3 ]^2=(23+8根号7)/9

(x^4+x^2+1)/x^2=x^2+1+1/x^2=(23-8根号7)/9+1+(23+8根号7)/9=46/9+1=55/9

所以,x^2/x^4+x^2+1=9/55