... ( ) ( )2 1 12x 1 2x 2 2x 1 2x 1 12 2 = + = + ( ) ( )2 1 12x 1 2x 2 2x 1 2x 1 12 2 = = Khi đó (1) ( ) ( )2 2 1 12x 1 1 2x 1 1 1 2 2 + + =2x 1 1 2x 1 1 2 + + =Ta thấy:323.3. ... 0502x 1 1 2x 1 12x 1 1 khi x 1 2x 1 1 1 1 2x 1 khi x 1 2 + = + + = < <ã Nếu x 1 thì (1) 22x 1 = 2 2x 1 = 22 2x - 1 = 1 2 x = 34. Do x = 34 < 1 nên ... 75 4x 11 x 11 + =+ +Đặt t = 2x 6x 7x 11 + 0, ta đợc:t2 + 4t - 5 = 0, t 0. t = 1. Với t = 1 2x 6x 7x 11 + = 1 x2 - 6x - 7 = x + 11 . x2 - 7x - 18 = 0 (x - 9) (x...