®Ò 15 (57) C©u 1: Cho xyz = 1 vµ x+y+z = 1 1 1 x y z + + = 0 TÝnh gi¸ trÞ M = 6 6 6 3 3 3 x y z x y z + + + + C©u 2: Cho a ≠ 0 ; ± 1 vµ 1 2 1 2 3 1 2 1 11 ; ; 2 1 1 x xa x x x a x x − −− = = = + + + T×m a nÕu x 1997 = 3 C©u 3: T×m m ®Ó ph¬ng tr×nh cã nghiÖm ©m: ( 2) 3( 1) 1 1 m x m x + − − = + C©u 4: Víi n ∈ N vµ n >1 CMR: 1 1 1 1 1 2 1 2 2n n n < + + + < + + C©u 5: Cho M = 3x 2 - 2x + 3y 2 – 2y + 6x +1 T×m gi¸ trÞ M biÕt: xy = 1 vµ x y+ ®¹t gi¸ trÞ nhá nhÊt. C©u 6: T×m x, y ∈ N biÕt: 2 x + 1 = y 2 C©u 7: Cho ABCV (AB < AC). AD, AM lµ ®êng ph©n gi¸c, ®êng trung tuyÕn cña ABCV . §êng th¼ng qua D vµ vu«ng gãc víi AD c¾t AC t¹i E So s¸nh S ADMV vµ S CEMV . ®Ò 15 (57) C©u 1: Cho xyz = 1 vµ x+y+z = 1 1 1 x y z + + = 0 TÝnh gi¸ trÞ M = 6 6 6 3 3 3 x y z x