a的平方+a-1=0,求2a的立方+4a的平方+1998=

a²+a-1=0
a²+a=1
原式=2a³+2a²+2a²+1998
=2a(a²+a)+2a²+1998
=2a*1+2a²+1998
=2a²+2a+1998
=2(a²+a)+1998
=2*1+1998
=2000