(ac+bd)(a/c+b/d)≤{(a+b)^2(c+d)^2}/4cd
等价于：
4(ac+bd)(ad+bc)≤(a+b)^2(c+d)^2
4(ac+bd)(ad+bc)≤[(a+b)(c+d)]^2
4(ac+bd)(ad+bc)≤[(ac+bc+ad+bd]^2
4(ac+bd)(ad+bc)≤[(ac+bd)+(ad+bc)]^2
等价于
[(ac+bd)+(ad+bc)]^2－4(ac+bd)(ad+bc)≥0
[(ac+bd)-(ad+bc)]^2≥0
这个式子显然是成立的,得证!