f'=df(x)/dx=x^2+2ax+5
x=-a
1.-a<=1,a>=-1,f'(1)=1+2a+5=2a+6>=0,a>=-3,a>=-1,f'(3)=9+6a+5=6a+14<=0,a<=-7/3,kongji,a>=-1
2.-a>=3,a<=-3,f'(3)=6a+14>=0,a>=-7/3,kongji
f'(1)=2a+6<=0,a<=-3,
zongshang,a>=-1,a<=-3