a=3次根号[4(√5+1)]
b=3次根号(4(√5-1)
所以a³-b³=8
ab=3次根号4*4²=4
x³+12x
=(a-b)³+12(a-b)
=a³-3a²b+3ab²-b³+12(a-b)
=8-3ab(a-b)+12(a-b)
=8-12(a-b+12(a-b)
=8