即a²-1=-a两边除以aa-1/a=-1两边平方a²-2+1/a²=1a²+1/a²=3a²+1/a²=3两边平方a^4+2+1/a^4=9a^4+1/a^4=7(a+1/a)²=a²+2+1/a²=3+2=5所以a+1/a=±√5
