已知函数f(t)对任意实数x、y都有f(x+y)=f(x)+f(y)+3xy,且f(1)=1.
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(1)若t∈N*,求f(t)的表达式;
(2)对t∈N*,不等式f(t)≥mt恒成立，求实数m的取值范围.
(n≥2).
}是等差数列；
)2（n∈N*），求{an}及Sn.
求
.