题干

已知数列{an},a2=2,an+an+1=3n,n∈N*,则a2+a4+a6+a8+a10+a12=____
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同类题4

根据材料内容,从方框中选择合适的句子填入文中空白处,使材料完整、通顺。其中有一个句子是多余的。

C

    In this week's Students Around the World ,Kim talks with Lisa Conroy, a college student from the USA,about her expenses(花费).

(K=Kim;L=Lisa)

K:Thanks for talking with me today, Lisa.____

L:Well.I'm twenty—one,and I'm studying at a university in Chicago.

K:____

L:My expenses for every term are almost$15,000.At the start of each term parents pay the $10,000 tuition(学费).I also get$2,000 from my college.I have to earn(挣)$3,000 myself.

K:How do you do that?

L:I have a part—time job at a hotel.I work about twenty hours a week,and cam$300.

K:____

L:It helps to pay for my rent(房租)and meals at college.It also pays for things like my phone,books,and clothes.

K:____

L:That's true! My mother advised me to spend my money carefully so I don't have to borrow.I hardly ever go to the movies.My roommates and I usually watch movies online,so it's cheaper.

K:____

L:I don't go to restaurants.I cook with my roommates so it's cheaper to eat.I try to walk or ride my bicycle to college. Oh,and I buy a lot of my clothes at second-hand stores.You can find some very cheap,nice clothes in those stores.

A.How else do you save(节省)money?

B.How do you spend that money?

C.Could you tell us a little about yourself?

D.Do you often ask for money from your parents?

E.How are you paying for your college education?

F.You don't use much money for fun,do you?

同类题5

阅读短文,回答问题:

    电热膜是一种新型的电热器件,如图甲所示是一种常见的电热膜.电热膜是在绝缘的聚酯薄膜表面,经过特殊工艺加工形成的一条条薄的导电墨线,导电墨线两端与金属导线相连,形成网状结构,其内部结构如图乙所示.

    电热膜通电工作时没有发红、炽热现象产生,它与被加热物体直接接触,产生的热量很快传给被加热物体,所以电热膜本身温度并不太高,不易氧化,使用寿命长.在制造电热膜时,会出现不同区域导电墨线厚度不均匀的现象,厚的导电墨线电阻小.导电墨线电阻随温度变化的关系如图丙所示,这种温度特性的优点是,它不会因厚度不均匀而出现严重发热不均、局部过热的现象,这是电热丝所不具备的,它保证了电热膜各处的温度均匀.

(1)电热膜取暖器工作时,室内空气温度升高是通过____ 方式增加空气内能的;

(2)某根导电墨线的局部导电材料脱落,如图丁中A部分,这根导电墨线的电阻____ ;

A.变大     B.变小     C.不变     D.以上三种情况均有可能

(3)与传统的电热丝加热器相比,电热膜取暖器的发热效率高,原因是____ 

(4)将图戊中一块电热膜接入电路,正常工作时金属导线中A、B处电流分别为IA和IB,则IA____ IB;(填“<”、“=”或“>”)

(5)电热膜不会因厚度不均而出现局部过热的现象,原因是____