设正数x,y满足log2(x+y+3)=log2x+log2y,则x+y的取值范围是 ______.
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设正数x,y满足log2(x+y+3)=log2x+log2y,则x+y的取值范围是 ______.
∵正数x,y满足log2(x+y+3)=log2x+log2y,
∴log2(x+y+3)=log2xy,
∴x+y+3=xy,
又x2-2xy+y2≥0,
所以左右加上4xy得到x2+2xy+y2≥4xy,
所以xy≤
(x+y)2
4,
由x+y+3=xy得到x+y+3≤
(x+y)2
4,
设x+y=a即4a+12≤a2,
解得a为(-∞,-2]或[6,+∞).
根据定义域x,y均大于零所以x+y取值范围是[6,+∞).
故答案为:[6,+∞).
∴log2(x+y+3)=log2xy,
∴x+y+3=xy,
又x2-2xy+y2≥0,
所以左右加上4xy得到x2+2xy+y2≥4xy,
所以xy≤
(x+y)2
4,
由x+y+3=xy得到x+y+3≤
(x+y)2
4,
设x+y=a即4a+12≤a2,
解得a为(-∞,-2]或[6,+∞).
根据定义域x,y均大于零所以x+y取值范围是[6,+∞).
故答案为:[6,+∞).
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