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230问答网 > 已知函数f(x)=根号下4-x+lg(3x-9)的定义域为A,集合B={x|x-a＜0,a属于R}

已知函数f(x)=根号下4-x+lg(3x-9)的定义域为A,集合B={x|x-a＜0,a属于R}

2025-02-12 05:17:42

推荐回答（1个）

回答1：

由 4-x>=0 得 x<=4 ，
由 3x-9>0 得 x>3 ，
所以函数定义域为 A=（3，4] 。

由于 B=（-∞，a），所以
（1）当 a<=3 时，A∩B=Φ（空集）；
（2）3（3）a>=4 时，A∩B=（3，4] 。

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