Question

a的平方减3a加1等于0,求a的立方+3a的平方+a-5

Answer 1

应是a^2+a-1=0

a的立方+3倍a的平方+a-4

=a*(a^2+3a+1)-4

=a*(1-a +3a+1)-4

=a*(2+2a)-4

=2*（a+a^2)-4

=2*1-4

=-2