答：
x²-4x-1=0
x不等于0,两边同除以x得：
x-4-1/x=0
x-1/x=4
x³-1/x³
=(x-1/x)(x²+1+1/x²)
=(x-1/x)[(x-1/x)²+3]
=4*(4²+3)
=4*19
=76