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问题 解答题
若x1、x2是方程5x2-4x-1=0的两个根，且点A（x1，x2）在第二象限，点B（m，n）和点A关于原点O对称，求
m2+n2
m-n
的值．
答案

方程化为：（5x+1）（x-1）=0

5x+1=0或x-1=0

∴x1=-

1
5
，x2=1．

因为点A（x1，x2）在第二象限，所以x1＜0，x2＞0．

方程5x2-4x-1=0的两个根是x1=-

1
5
，x2=1．

又因为点B和点A关于原点对称，所以m=

1
5
，n=-1．

所以

m2+n2
m-n
=
(
1
5
)2+(-1)2
1
5
+1
=
26
25
6
5
=
13
15
=
195
15
．

阅读理解

阅读短文，判断下列句子的正误，与短文内容相符的在括号中写"Y"，不相符的写"N"。

    Hello, I'm Lucy. I have got a bike. I go to school by bike.  My mother has got a bike, and she goes to

work by bike, too. My father has got a car.  He goes to work by car. This is Ms Li. She is my English

teacher.  She walks to school.

(     ) 1. Lucy walks to school.

(     ) 2. Her father goes to work by taxi.

( ) 3. Her mother has got a bike.

(     ) 4. Ms Li goes to school by bus.
查看答案
填空题

有下列10种物质：空气、冰、汞、石灰水、红磷、干冰、铜绿、煤、大理石、甲烷

（1）属于混合物的是______．

（2）用化学式回答：属于单质的是______．属于氧化物的是______．属于有机物的是______．
查看答案