Chän kÕt qu¶ ®óng a. (x - 1)2 bằng: A, x2 + 2x -1; B, x2 + 2x +1; C, x2 - 2x -1; D, x2 - 2x +1. b. (x + 2)2 bằng: A, x2 + 2x + 4; B, x2 - 4x + 4; C, x2 + 4x + 4; D, x2 - 4x + 4. c. (a - b)(b - a) bằng: A, - (a - b)2; B, -(b + a)2; C, (a + b)2; D, (b + a)2. d. - x2 + 6x - 9 bằng: A, (x- 3 )2; B, ; - (x- 3 )2 C, (3 - x )2; D, (x+ 3 )2