(1)n=2时：设a1,a2为实数,有（a1-a2）²≥0,（当a1=a2时,等号成立）a1²-2a1a2+a2²≥0,a1²+a2²≥2a1a2,a1²+2a1a2+a2²≥4a1a2,（a1+a2)²/4≥a1a2,∴（a1+a2)/2≥√a1a2.(2)设n...