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问题 选择题
已知关于x的方程2x2-2mx-4=0的两根为x1、x2，且
1
x1
+
1
x2
=2，那么实数m的值等于（　　）
A．4B．-4C．8D．-8
答案

∵x的方程2x2-2mx-4=0的两根为x1、x2

∴x1+x2=-

b
a
=m，x1x2=
c
a
=-2

∵

1
x1
+
1
x2
=2

∴

x1+x2
x1•x2
=
m
-2
=2

解得m=-4．

故选B．

材料分析题

明智中学八年级5班是先进集体。这个班具有良好的班风，有一股永不服输的豪气。在与兄弟班的竞争中，大家心往一处想，劲往一处使，各项工作都做得有声有色。班上同学各有自己的目标，大家在学习中开展竞争，你追我赶，各显神通，互相帮助，成绩都很优秀。

（1）八年级5班的同学在合作中竞争的成功经验，对你有什么启发。

                                                                                                                                                              

                                                                                                                                                              

（2）我们在创建优秀班集体的过程中，如何处理同学间的竞争关系？ 

                                                                                                                                                              

                                                                                                                                                              

（3）由此有人说：竞争就是“你死我活”，合作就是“一团和气”，两者是水火不相容关系。请问：这种看法对吗？为什么？

                                                                                                                                                               

                                                                                                                                                               

                                                                                                                                                              

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单项选择题

下列哪种离子碎裂方式只适用于MALDI？（）

A.PSD

B.CID

C.ECD

D.ETD
查看答案