1.y=x+1/x²= x/2+ x/2+ 1/x²≥3[(x/2)(x/2)(1/x²)]^(1/3)=3•(1/4)^(1/3)=(3/2)•2^(1/3)
当且仅当x/2=1/x² 时,y有最小值为(3/2)•2^(1/3)
2.y=x²+3/x = x²+3/2x +3/2x≥3[x²(3/2x)(3/2x)]^(1/3)=(3/2)•18^(1/3)
当且仅当x²=3/(2x) 时,y有最小值为(3/2)•18^(1/3)