a,b是方程x平方-x-1=0的2个实数根
a²-a-1=0 即a²=a+1
a+b=1,ab=-1
a^4+3b
=﹙a²﹚²+3b
=(a+1)²+3b
=a²+2a+1+3b
=a+1+2a+1+3b
=3(a+b)+2
=3×1+2
=5