(1)y=b,x=-b/ks=0.5*b*(-b/k)=b-b/k+3-b*b=2kb-2b+6kk=(2b-b*b)/(2b+6)(2)s=b-b/k+3=b-(2b+6)/(2-b)+3=(2b-b*b-2b-6+6-3b)/(2-b)=(b*b+3b)/(b-2)=((b*b-4b+4)+(7b-14)+10)/(b-2)=(b-2)+7+10/(b-2)>=2根号10+7最小为2根号10+7
