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问题 填空题
在下 * * 个函数中，①y=2x，②y=log2x，③y=x2，④y=x-1，⑤y=cos2x．当0＜x1＜x2＜1
时，使f(
x1+x2
2
)＞
f(x1)+f(x2)
2
恒成立的函数是______（将正确序号都填上）．
答案

∵f(

x1+x2
2
)＞
f(x1)+f(x2)
2
；表示连接两点A（x1，f（x1）），B （x2，f（x2））的线段的中点纵坐标小于f（x）在曲线AB中点 (
x1+x2
2
，f(
x1+x2
2
))；的纵坐标，

也就是说f（x）的图象“上凸”．所以只需判断哪个函数的图象“上凸”即可．

由图形可直观得到：①③④⑤的图象都不是上凸的，只有②为“上凸”的函数．

故答案为：②．

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The United States has what is called (38) . Tax rates increase as (39) increase. This year, people earning more than (40) are taxed at the highest rate.
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Individuals who earn less than (42) pay no income tax. But they do pay (43) , Medicare and other taxes.
There are many different ways for people and businesses to reduce their (44) Most homeowners, for example, can reduce their taxes a little by reporting to the I.R.S. the interest they pay (45) . This is called a (46)
In 2004, personal income taxes provided the government with most of its money: (47) of the budget. Social security and other (48) taxes provided (49) . Other forms of income include (50) , money borrowed to (51) and special taxes on (52) .
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Preparing tax documents can be complex. The I.R.S. estimates that taxpayers need an average of about 13 hours to prepare tax documents. And that is just for the basic tax form. For business, the I.R.S. estimates an (54) needs more than 50 hours. This is why a lot of Americans pay (55) to complete their tax documents for them.
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单项选择题

关于原发性肾病综合征，以下哪项不正确

A．水肿常为最早出现的症状

B．水肿开始于眼睑

C．水肿处指压后凹陷不明显

D．由于肠道水肿可引起腹泻

E．水肿严重时可出现胸腹水
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