题目

Do you find getting up in the morning so difficult that it's painful? This might be called laziness, but Dr．Kleitman has a new explanation．He has proved that everyone has a daily energy cycle．        During the hours when you labor through your work you may say that you're “hot”．That's true．The time of day when you feel most energetic is when your cycle of body temperature is at its peak（高峰）．For some people the peak comes before noon．For others it comes in the afternoon or evening．No one has discovered why this is so, but it leads to such familiar monologues 19．已知函数f（x）=ax2-（5a-1）x+3a+1（a∈R）．（1）若f（x）在区间[1，+∞）上是单调增函数，求a的取值范围； （2）在（1）的条件下，若函数f（x）在区间[1，5]上有零点，求a的取值范围．