3.若函数f(x)=x2+2(a−1)x+2f(x)=x^{2}+2(a-1)x+2f(x)=x2+2(a−1)x+2在区间(−∞,3)(-\infty ,3)(−∞,3)上是单调函数,则实数aaa的取值范围是((( )))