§Ò 36 (78) C©u 1: a, Cho a+b+c = 0 vµ a 2 + b 2 + c 2 = 14. T×m gi¸ trÞ B = a 4 +b 4 +c 4 . b, Cho x > 0 vµ x 2 + 2 1 x = 7. CMR: x 5 + 5 1 x lµ sè nguyªn. C©u 2: Cho a, b, c > 0. CMR: 3 3 3 a b c ab bc ca b c a + + ≥ + + C©u 3: Cho a, b, c > 0 vµ a+b+c = 1. T×m gi¸ trÞ nhá nhÊt: A = 2 2 2 1 1 1 ( ) ( ) ( )a b c a b c + + + + + C©u 4: X¸c ®Þnh a, b sao cho f(x) = ax 4 +bx 3 +1 chia hÕt cho g(x) = (x-1) 2 . C©u 5: T×m nghiÖm nguyªn cña PT: 1 1 1 1 x y z + + = C©u 6: CHo ABCV , trung tuyÕn AM. Qua D thuéc BC vÏ ®êng song song víi AM c¾t AB, AC t¹i E, F. a, CMR: Khi D di ®éng trªn BC th× DE + DF cã gi¸ trÞ kh«ng ®æi. b, Qua A vÏ ®êng th¼ng song song víi BC c¾t EF t¹i K. CMR: K lµ trung tuyÕn cña EF. . §Ò 36 ( 78) C©u 1: a, Cho a+b+c = 0 vµ a 2 + b 2 + c 2 = 14. T×m gi¸ trÞ B = a 4 +b 4 +c 4 . b, Cho