(1)y=b,x=-b/k
s=0.5*b*(-b/k)=b-b/k+3
-b*b=2kb-2b+6k
k=(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
(1)y=b,x=-b/k
s=0.5*b*(-b/k)=b-b/k+3
-b*b=2kb-2b+6k
k=(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