已知 mi∈Rm_i∈Rmi∈R ∑i=12019 mi=0\sum_{i = 1}^{2019} \ m_i=0∑i=12019 mi=0 ∑i=12019 mi2=1\sum_{i = 1}^{2019} \ m_i^2=1∑i=12019 mi2=1
若 a=minm1,m2.....m2019a=min_{ m1,m2.....m2019}a=minm1,m2.....m2019 b=maxm1,m2.....m2019b=max_{ m1,m2.....m2019}b=maxm1,m2.....m2019 求证 a∗b<=−1/2019a*b<=-1/2019 a∗b<=−1/2019
