... t í n h loi 2? (x,/i(a;)) 125 Ị L ấ y (zi,oti) € c *2 {i = 1 ,2) v À G [0,1], t a có: < = • =*> - /,-(*) < X Ĩ + x , - X > < /l (2) + X* + x* € ỡ ( / ! + / ) ( x ) = • 2 ( i = Ì , 2) /2( ^)-(/,(x)+/ (x)) ... n h lý 4.1 v (4 .22 ) suy ^ Chọn s (4 .23 ) ra: > sup{< z ,.v > : r e Ọ } + e D o b ấ t d ẳ n g t h ứ c Jensen v (4 .23 ), (Ì - t)f(*, /(s ,x + fx) t , s„ \:i -2 Vì vậy, (Ì - t...