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问题 解答题

已知关于x的一元二次方程 （m∈Z）①mx2-4x+4=0； ②x2-4mx+4m2-4m-5=0，求方程①和②都有整数解的充要条件．

答案

∵两方程都有解，

∴△1=16-16m≥0，△2=16m2-4（4m2-4m-5）≥0，

∴-

5
4
≤m≤1，又m∈Z，∴m=-1，0，1

经检验，只有当m=1时，两方程才都有整数解．

即方程①和②都有整数解的充要条件是m=1．

单项选择题

光驱型号DVD-RW中的“W”表示（）

A.高级

B.速度快

C.可刻录

D.可重播
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单项选择题

Charles liked music very much when he was at school, but (41) he went to the university he decided to study medicine (42) music. When he passed his examinations and became a doctor, he had to work in a hospital for (43) . There he discovered that a lot of patients were happier if (44) music was played for them. When Charles got an office and began to work (45) himself, he decided to (46) his patients happy by having a tape recorder in his waiting room play beautiful music for them.
But (47) the tape recorder had been put in(安装), Charles’ nurse heard a woman complain in the crowded (48) , "Here we’re (49) waiting to see the doctor, and he’s just playing (50) piano in his office instead of doing his work. \

[A]instead of[B]because of[C]in spite of
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