【单选题】【消耗次数：1】
等差数列{an}的首项a?=1，公差d=3，当an=31时，项数n等于（ ）
①
11
②
12
③
10
④
9
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相关题目
【简答题】
设{an}是公比为 q 的等比数列，且a1，a3，a2成等差数列．(1)求q的值；(2)设{bn}是以2为首项，q为公差的等差数列，其前n项和为Sn，当n≥2时，比较Sn与bn的大小，并说明理由．
【单选题】
等差数列0，-3，-6，······的通项公式是( )
①
<img src="20190809/1565314218197257.png" title="1565314218197257.png" alt="图片5.png"/>
②
<img src="20190809/1565314240415972.png" title="1565314240415972.png" alt="图片6.png"/>
③
<img src="20190809/1565314247141241.png" title="1565314247141241.png" alt="图片7.png"/>
④
<img src="20190809/1565314264699167.png" title="1565314264699167.png" alt="图片8.png"/>
【单选题】
关于等差数列的概念，描述正确的是哪一项（ ）
①
一般地，如果一个数列，每一项与它的前一项的差都等于常数，那么这个数列叫等差数列
②
一般地，如果一个数列，从第二项起，每一项与它的前一项的差都等于常数，那么这个数列叫等差数列
③
一般地，如果一个数列，从第二项起，每一项与它的前一项的差都等于同一个常数，那么这个数列叫等差数列
④
一般地，如果一个数列，每一项与它的前一项的差都等于同一个常数，那么这个数列叫等差数列
【单选题】
等差数列<img class="kfformula" src="20190809/1565315219717157.png" data-latex="\left \{ {{a}_{n}} \right \} "/>首项<img class="kfformula" src="20190809/1565315219801596.png" data-latex="{a}_{1}=1"/>，公差<img class="kfformula" src="20190809/1565315219560191.png" data-latex="d=-3"/>，当<img class="kfformula" src="20190809/1565315219192999.png" data-latex="{a}_{n}=-56"/>时，项数<img class="kfformula" src="20190809/1565315219715609.png" data-latex="n"/>等于（ ）
①
18
②
19
③
20
④
21
【简答题】
已知方程(x2－2x＋m)(x2－2x＋n)＝0的四个根组成一个首项为1/4的等差数列，求｜m－n｜的值．
【单选题】
等差数列<img class="kfformula" src="20190809/1565317844150977.png" data-latex="\left \{ {{a}_{n}} \right \} "/>的首项<img class="kfformula" src="20190809/1565317844698638.png" data-latex="{a}_{1}=-2"/>，<img class="kfformula" src="20190809/1565317844536248.png" data-latex="{S}_{3}=3"/>，那么（ ）
①
<img class="kfformula" src="20190809/1565317844862924.png" data-latex="d=3"/>
②
<img class="kfformula" src="20190809/1565317844935823.png" data-latex="d=2"/>
③
<img class="kfformula" src="20190809/1565317844903124.png" data-latex="d=-2"/>
④
<img class="kfformula" src="20190809/1565317844953331.png" data-latex="d=-3"/>
随机题目
【单选题】
A: I got a job from Dell B: Thats great news. Im very happy for you. A: Thanks. I feel like celebrating. Lets go have a beer. [填空].
①
Its on me
②
Its so fine today
③
Its your turn
④
It is rather expensive
【单选题】
A: Richard, class begins at 9, and you are late. B: I know, but I missed my bus, Im sorry. B: [填空]. You have to be here on time.
①
Thats no excuse
②
Dont mention it
③
You neednt be
④
No problem
【单选题】
A: Dont tell me youve got a headache again. B: [填空].
①
Sorry, I wont be late next time
②
Youre right, Im just joking
③
All right, I wont say it
④
OK, youve made your point
【单选题】
A: Im sorry. Those shoes are not available in your size. B: [填空].
①
No use saying sorry. Thats a real let down
②
Im truly grateful for your help
③
Its just as Ive expected
④
Thats a pity. Thank you anyway
【单选题】
A: [填空]? B: Yes, Id like to open a savings account.
①
What do you want to do, sir
②
Why have you come here
③
Do you have anything to do here
④
Can I help you, sir
【单选题】
A: Bill told me he could not come here because his father was ill. B: [填空]
①
Its good.
②
Thats bad.
③
He is impolite.
④
What a pity!
【单选题】
A: Do you know Marks phone number? B: [填空] . A: OK. I might as well look it up in the phone book.
①
Just a second
②
Not that I know of
③
I cant think of it now
④
Why ask?
【单选题】
A: How long can I keep the book? B: [填空].
①
Any period longer than four weeks, you will be fined
②
Four weeks, but you can renew it if you need it longer
③
You can check it on the computer over there
④
At most four weeks if you dont mind
【单选题】
A: Is it time for us to set off now? B: [填空]. We’ll have to wait for one more hour.
①
Certainly, it is
②
Thats all right
③
Sorry, I am afraid not
④
Sorry,its too long
【单选题】
A: We had a trip to China this summer. B: [填空] A: Yes, we did. In fact, we even encountered a lion.
①
Didnt you?
②
How did it go?
③
I guess you did.
④
I bet you had a great time.