高一对数题
函数y=log2(x)+logx(2x)的值域是
答案是(负无穷,-1)并上(3,正无穷)
请给解题过程,谢谢!
人气:219 ℃ 时间:2020-02-06 05:12:47
解答
令a=log2(x)
即a=lgx/lg2
则logx(2x)=logx(2)+logx(x)=lg2/lgx+1=1/a+1
所以y=a+1/a+1
这里a≠0
所以a>0
a+1/a≥2√(a*1/a)=2
同理a
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