Giải thích các bước giải:
k) (x – 1)(x – 3) – (4 – x)(2x + 1) – 3x2 + 2x – 5
= x2 – 3x – x + 3 – ( 4 – x ) . ( 2x + 1 ) – 3x2 + 2x – 5
= x2 – 3x – x + 3 – ( 8x + 4 – 2x2 – x ) – 3x2 + 2x – 5
= x2 – 3x – x + 3 – ( 7x + 4 – 2x2 ) – 3x2 + 2x – 5
= x2 – 3x – x + 3 – 7x – 4 + 2x2 – 3x2 + 2x – 5
= 0 – 3x – x + 3 – 7x – 4 + 2x – 5
= 0 – 9x + 3 – 4 – 5
= 0 – 9x – 6
= – 9x – 6
