9. (2023春•临沂期中)函数f(x)=x3+3ax2+bx+af(x)=x^{3}+3ax^{2}+bx+af(x)=x3+3ax2+bx+a在x=−1x=-1x=−1时有极大值0,则a+b=(a+b=(a+b=( )))