Question

几何平均不等式5若x>0,则4x+(9/x²)的最小值是?

Answer 1

4x+(9/x^2)

=2x+2x+(9/x^2)

>=3*根号下3次方（2x*2x*(9/x^2))

=3*根号下3次方18

等号成立2x=9/x^2得x=根号下3次方（9/2)