设a2+a-1=0,求2a3+4a2+1998的值.

问题描述:

设a2+a-1=0,求2a3+4a2+1998的值.

∵a2+a-1=0,
∴a2+a=1,
∴2a3+4a2+1998
=2a3+2a2+2a2+1998
=2a(a2+a)+2a2+1998
=2a×1+2a2+1998
=2(a2+a)+1998
=2+1998
=2000