给出下列四个命题: ①若a>b>0,c>d>0,那么 a d < b c ;②已知a、b、m都是正数,并且a<b,则 a+m b+m > a b ;③若a、b∈R,则a 2 +b 2 +5≥2(2a-b);④函数f(x)=2-3x- 4 x 的最大值是2-4 3 .其中正确命题的序号是______把你认为正确命题的序号都填上)
【简答题】Case 1: Litz is a professor of cross—cultural communication in a university in Finland. She invited her Chinese students home for an evening party. The schema from Litz’s point of view includes the fo...