(i) 12x² - 7x + 1

= 12x² – 4x – 3x + 1

= 4x (3x – 1) – 1 (3x – 1)

= (3x – 1) (4x – 1)

(ii) 2x² + 6x + x + 3

= 2x (x + 3) + 1 (x + 3)

= (x + 3) (2x + 1)

(iii) 6x² + 5x – 6

= 6x² + 9x – 4x – 6

= 3x (2x + 3) – 2 (2x + 3)

= (2x + 3) (3x – 2)

(iv) 3x² – 4x + 3x – 4

= x (3x – 4) + 1 (3x – 4)

= (3x – 4) (x + 1)