高中数学,函数的恒成立问题,求参数的取值范围,必采纳谢谢!!

2025-05-14 11:28:37
推荐回答(1个)
回答(1):

16.
(1)
h(x)=[f(x)+1]·g(x)
=[3-2log2(x)+1]·log2(x)
=-2[log2(x)]²+4log2(x)
=-2[log2(x)]²-4log2(x)-2+2
=-2[log2(x) -1]²+2
x∈[1,4],则0≤log2(x)≤2
log2(x)=1时,h(x)取得最大值。h(x)max=2
log2(x)=0或log2(x)=2时,h(x)取得最小值。h(x)min=-2+2=0
函数h(x)的值域为[0,2]
(2)
f(x²)·f(√x)>k·g(x)
[3-2log2(x²)][3-2log2(√x)]>k·log2(x)
[3-4log2(x)][3-log2(x)]>k·log2(x)
4[log2(x)]²-(k+15)log2(x)+9>0
x∈[1,4],则0≤log2(x)≤2
令log2(x)=t,0≤t≤2
令h(t)=4t²-(k+15)t+9,(0≤t≤2)
对称轴t=(k+15)/8
顶点纵坐标=[144-(k+15)²]/16
(k+15)/8<0时,即k<-15时,h(x)单调递增
t=0时,h(x)min=9>0
0≤(k+15)/8≤2时,即-15≤k≤1时
[144-(k+15)²]/16>0
(k+15)²<144
-27(k+15)/8>2时,即k>1时,h(x)单调递减
t=2时,h(x)min=4·2²-(k+15)·2+9>0
2k+5<0
k<-5/2(舍去)
综上,得:k<-3
k的取值范围为(-∞,-3)