f(x)=(x-2)²-8
开口向上,对称轴为x=2
当1<=t<=2时,对称轴在[t,t+1]内,则最小值g(t)=f(2)=-8;
当t>2时,对称轴在[t,t+1]左边,函数在此区间单调增,最小值为g(t)=f(t)=t²-4t-4;
当t<1时,对称轴在[t,t+1]右边,函数在此区间单调减,最小值为g(t)=f(t+1)=t²-2t-7.