分解因式：3a+3b=______．
找到3a与3b的公因式3，
利用提公因式法即可解答．
3a+3b=3（a+b）．
故答案为：3（a+b）．
函数f（x）=x3-3x2+1在x=______处取得极小值．
After using a C02 portable extinguisher,it should be（）.
A.put back in service if some CO2 remains
B.hydrostatically tested
C.retagged
D.recharged
