3a方=1+a 6a方=2a+2
6a的三次方+7a的平方-5a+2004
=a(6a方+7a-5)+2004
=a（2a+2+7a-5）+2004
=9a方-3a+2004
=3（3a方-a）+2004
=3*1+2004
=2007