因为abc=1
所以,1/a+1/b+1/c
=abc/a+abc/+abc/c
=bc+ac+ab
=1/2(ab+bc+bc+ca+ca+ab)
＞1/2[2(ab^2c)^(1/2)+2(bc^2a)^(1/2)+2(a^2bc)^(1/2)] (因为abc不全相等,所以不能取等号)
=1/2[2*b^(1/2)+2*c^(1/2)+2*a^(1/2)](因为abc=1)
=b^(1/2)+c^(1/2)+a^(1/2)