Hoặc
b) Rút gọn A.
b) A=x+2x+3−5x+3x−2+12−x
=x+2x−2x+3x−2−5x+3x−2−x+3x+3x−2
=x2−4−5−x−3x+3x−2=x2−x−12x+3x−2
=x+3x−4x+3x−2=x−4x−2.