诺A方-2A-1=0,求代数式A四次=A四次分之一的值

方程两边同除以A
A-2-1/A=0
A-1/A=2
A^4+1/A^4
=(A^2+1/A^2)^2-2
=[(A-1/A)^2+2]^2-2
=(2^2+2)^2-2
=36-2
=34

34

应该是A^4-1/A^4哦？由已知得：A-1/A=2，A^2+1/A^2=6，A+1/A=正负2倍根2
A^4-1/A^4=(A^2+1/A^2)(A+1/A)(A-1/A)
=正负24倍根2