Hoặc
d) a2+3a−2−3aa−2+a−12−a.
d) a2+3a−2−3aa−2+a−12−a=a2+3a−2−3aa−2+1−aa−2
=a2+3−3a+1−aa−2=a2−4a+4a−2=(a−2)2a−2=a−2.