6．某种商品零售价经过两次降价后的价格为降价前的，

则平均每次降价(　　 )

A．　　　　 B．　　　　　　　 C．　　　　　　 D．

5．在正方形网格中，的位置如图2所示，则的值为(　　 )

A．　　　　　　 B．　　　　 C．　　　　 D．

4．下列说法正确的是( 　　)

A．的平方根是　　　　　　　 B．将点向右平移5个单位长度到点

C．是无理数　　　　　　　　　 D．点关于轴的对称点是

3．如图1，已知与相交于点，，如果

，，则的大小为(　　 )

A．　　　　　 B．　　　　 C．　　　　 D．

2．下列运算正确的是(　　 )

A．　　　　　　 B．

C．　　　　　 D．

1．2的相反数是(　　 )

A．　　　　　　　 B．　　　　　 C．　　　　　 D．

19．解：(1)从计算器中随机抽取一个，再从保护盖中随机取一个，有Aa，Ab，Ba，Bb四种情况．

恰好匹配的有Aa，Bb两种情况，

．····························································································· 2分

(2)用树形图法表示：

所有可能的结果AB　 Aa　 Ab　 BA　 Ba　 Bb　 aA　 aB　 ab　 bA　 bB　 ba······················ 4分

可见，从计算器和保护盖中随机取两个，共有12种不同的情况．

其中恰好匹配的有4种，分别是Aa，Bb，aA，bB，

．··························································································· 6分

或用列表法表示：

　　　　　　　　　　　　　　　　　 ·········································································· 6分

可见，从计算器和保护盖中随机取两个，共有12种不同的情况．

其中恰好匹配的有4种，分别是Aa，Bb，aA，bB，

．··························································································· 6分

18．解：(1)符合条件的点的坐标分别是

，，．··············································································· 3分

(2)①选择点时，设直线的解析式为，

由题意得　 解得·········································································· 5分

直线的解析式为．············································································ 6分

②选择点时，类似①的求法，可得

直线的解析式为．················································································· 6分

③选择点时，类似①的求法，可得直线的解析式为．············ 6分

说明：第(1)问中，每写对一个得1分．

17．解：原式················································································· 2分

········································································································· 3分

．···················································································································· 4分

当时，原式．······································································ 6分

13．　　　　　　 14．，　　　　　 15．4　　　　　　 16．①②③

说明：第16题，填了④的，不得分；未填④的，①，②，③中每填一个得1分．