令a=√(x+3)
則a≥0
x=a²-3
所以y=f(x)=a²-3+a
=(a+1/2)²-13/4
a≥0
所以a=0
最小值是-3???????????????????f(x)=x+????x??+3????С???????x=0????С??3????x=t??t>=0??y=t^2+t+3t=-b/2a=-1/2,ymin=11/4?????????????????????Σ?????t??0????????????????????????????????????????????????л?????лл??