DE THI HSG TOAN 9 _ 2012 - 2013 TP HA NOI

         4 3 2 P(x) 4x 11x 2ax 5bx 6 = − − + −   2 Q(x) x 2x 3 = − −   ( ) ( ) 2013 2012 2011 2013 201 2 2011 P a 8a 11a b 8b 11b= − + + − +   !"# a 4 5, b 4 5 = + = −   $%&'()* 2 2 2 2 6x y xy 5x 5y 6 0 20x y 28x 9 0  − − + + − =   − − + =    +,-+%.'()* 2 2 6 x 10y 2xy x 28y 18 0 + + − − + =   /() a, b, c %. 1 2 3 3 a b c + + =  * 2 2 2 2 2 2 2 2 2 27a b 8c 3 2 c(c 9a ) a(4a b ) b(9b 4c ) + + ≥ + + +    ABC 0 0123'(45 (O)   AB AC <  (4 AD, BE, CF ! ABC 6'78$19:(4; EF, CB  <(4; AI = (O) 7>#? @ A, M, F, H, E AB,3(45 $1C: BC  M, H, N ;  BM.AC AM.BC AB.MC + =    2013  1 2 2 013 A , A , , A (45 ( ) O, 1 DEAB36';   , (4 5 ( ) O, 1  02  :F 0   (G 3  >   1 2 2013 MA MA MA 2013 + + + ≥  H       . 5bx 6 = − − + −   2 Q(x) x 2x 3 = − −   ( ) ( ) 2013 2012 2011 2013 201 2 2011 P a 8a 11a b 8b 11b= − + + − +   !"# a 4 5, b.   $%&'()* 2 2 2 2 6x y xy 5x 5y 6 0 20x y 28x 9 0  − − + + − =   − − + =    +, - +%.'()* 2 2 6 x 10y 2xy x 28y 18 0 + +. b, c %. 1 2 3 3 a b c + + =  * 2 2 2 2 2 2 2 2 2 27a b 8c 3 2 c(c 9a ) a(4a b ) b(9b 4c ) + + ≥ + + +    ABC 0 0123'(45 (O) 