Page 114 - Fixtures
P. 114
@ @YY@ @ÖïÐaínÜaì@Þî†bjnÜa@ @
. 6
.CD BD BC AD AC AB
A<B <C <D
:
AD : ACBD AC : ADBC AB : ACBD
BD : BDAC BC : BCAD
.CD : CDAB
.0 .5
.C(9, 3) . 5C(9, 4) = 5 × 9! = 630
.
4!×5!
.
.0 < B <C < D
.CD0B BD0C BC 0D
. 3C(9, 3) = 3 × 9! = 252
3!×6!
. 630 + 252 = 882
. [AIME 1989] ( )
