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函数y=log2x+logx(2x)的值域是______.
人气:342 ℃ 时间:2020-01-24 12:39:18
解答
∵y=log2x+logx(2x)=log2x+logxx+logx2
=log2x+logx2+1=log2x+
1
log2x
+1

令t=log2x,∵x>0且x≠1,∴t>0或t<0.
t+
1
t
≥2
,或t+
1
t
≤−2

∴y=t+
1
t
+1≤-1,或y≥3,
故答案为:(-∞,-1]∪[3,+∞).
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