229 de thi thu THPTQG nam 2018 mon toan THPT chuyen dong bang song hong lan 1 file word co loi giai chi tiet

... có 10 00 chữ số 10 999 �S 10 1000 Cách giải: S    C10  C02   C0n    C 11  C12   C1n     C nn  11  C nn 1   C nn S    C 10  C 11    C 02  C12  C 22    C30  C13...  a  b ��  2; � � y t  t  1 2  t  t 1 1 t 1 t 1 t 1 0t� Nếu t  1 � 2 t 1 y 2 Nếu 1 t  1 � 0�� �� t 22� t 2 t 1 t 1 t 1 2 t 1 y 2 Vậy y �2  Dấu xảy �  ... Ta có � 1 ; u �  3;3 ;1 uuuuuur Lấy M1  1; 0;0  �d1 ; M  1; 2; m  �d � M1M   0; 2; m  � d  d1 ;d  uuuuuur uu r uur � M1M � u m  1 � 1 ; u �  m    �� � S   1; 11  uu r uur