Yet most users report they spend about same amount of time they always have in other activities such

题目

Yet most users report they spend about same amount of time they always have in other activities such as the evening meal and playing sports
这道题 是have in other activities 中in有问题,但不知为什么?请童鞋们帮帮忙这道题

答案

这个函数是开口向上的二次函数
所以最大值只可能在区间两端取得
又对称轴xo=-a/2
当xo 离区间左端较近时 即 -1<a<0
当x=1时 有最大值……
当xo离区间右端点较近时 即 a<=-1
当x=0时 有最大值……
分别代入就可以了 注意a<0