当a≥0时，化简：3a2=______，当m＜3时，(m-3)2=______．_爱下问搜题

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问题填空题

当a≥0时，化简：

3a2

=______，当m＜3时，

(m-3)2

=______．

答案

（1）∵a≥0，∴

3a2

=

3

|a|=

3

a；

（2）∵m＜3，∴m-3＜0；故原式=-（m-3）=3-m．

完形填空

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单项选择题

声频在16Hz-20Hz之间的称之为()。

A、次声

B、可闻声

C、超声

D、X线

E、可见光