(3x−2)5=C50(3x)5+C51(3x)4.(−2)+C52(3x)3.(−2)2+C53(3x)2.(−2)3
+C54(3x).(−2)4+C55(−2)5
=243x5−810x4+1080x3−720x2+240x−32
Hệ số x3 trong khai triển (3x−2)5 là 1080