f(1)=a+4+3a=0,a=-1,
f(x)=-x²+4x-3,对称轴为x=2,
(1)当t≤1时,t+1≤2,区间[t,t+1]在对称轴的左边,f(x)是增函数,最大值为f(t+1)=-t²+2t;
(2)当1