- 1×a=-4/(√5- 1)
That is-a =-4 (√ 5+1)/(√ 5-1) (√ 5+1).
That is, a=√5+ 1
Therefore, a 3-2a 2-4a
=a(a^2-2a-4)
=a[(a- 1)^2-5]
=(√5+ 1)[(√5+ 1- 1)^2-5]
=(√5+ 1)[(√5)^2-5]
=(√5+ 1)×0
=0