Ta có
+) 15 x 2 + 10xy = 5x.3x + 5x.2y = 5x(3x + 2y)
+) 35x(y – 8) – 14y(8 – y) = 7.5x(y – 8) + 7.2(y – 8)
= (7.5x + 7.2y)(y – 8) = 7(5x + 2y)(y – 8)
+) -x + 6 x 2 – 12xy + 2 = (6 x 2 y – 12xy) – (x – 2)
= (6xy.x – 6xy.2) – (x – 2)
= 6xy(x – 2) – (x – 2)
= (6xy – 1)(x – 2)
+) x 3 – x 2 + x – 1= x 2 .x – x 2 + x – 1
= x 2 (x – 1) + (x – 1)
= ( x 2 + 1)(x – 1)
Vậy A, B, D đúng, C sai
Đáp án cần chọn là: C