所以an=a1+(n-1)d=-2+2(n-1)=2n-4.故答案为2n-4. 分别求出求出f(x-1)和f(x+1)得到a1和a3,然后利用等差中项的概念列式求得x的值,根据数列{an}是公差为正数的等差数列对首项及公差进行取舍,从而求出数列{an}的通项公式. 本题考点:等差数列的通项公式. 考点点评:本题考查了等差数列的通项公式,...
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举报 1、设等差为b则前十项和为10*a1+9b=145,得b=15,a2n=1+(2n-1)*15.2、-27/(-3)=9,则等比的平方为9,即:等比为-3或3;a=1,b=9,c=81(等比为-3)或a=-1,b=-9,c=-81(等比为3).3、(2a+2)*2=a*(3a+3),解得a=-1或-4;按... 解析看不懂?免费查看同类题视频解析查看解答 ...
An element (5) engageable with one or more other similar elements (5) is disclosed. The element includes a recess (10) in its outer surface for casting a concrete stringer (43) and reinforcements (15). The free end of at least one rigid bearing member (16) secured to said element (...
(2017·上海卷)已知a,b,c为实常数,数列{xn}的通项xn=an2+bn+c,n∈N,则“存在k∈N,使得x100＋k,x200＋k,x300＋k成等差数列”的一个必要条件是( )A.a≥0 B.b≤0 C.c=0 D.a-2b+c=0 答案：答案 A 解析 要使x100＋k,x200＋k,x300＋k构成等差数列,只需要2x200＋k=x100＋k+x300＋k,即2a...
If the transistor is used as an amplifying device, it is in a forward-active operating mode,or simply the active regionA.正确B.错误的答案是什么.用刷刷题APP,拍照搜索答疑.刷刷题(shuashuati.com)是专业的大学职业搜题找答案,刷题练习的工具.一键将文档转化为在线
The reports include an indication of a connection to or disconnection from one of the WiFi access points, a time of the connection or disconnection, and an identifier of the one of the WiFi access points. Data including connect times and disconnect times may be generated from the reports. ...