that deal in data, the oil of the digital age. The most valuable firms are Google,Amazon,这个问题由于涉及到老牛和小马的驮包裹的两个未知数，我们设老牛驮个包裹对宇宙未来的预言，其关键问题在于宇宙的平均密度是多少。Sport is not only physically challenging, but it can also be mentally精神上地) challenging. Criticism from coaches and other teammates, as well as pressure to win can create a great amount of stress for young athletes.等差数列的概念与通项公式
【思维导图】
【微试题】
a
1.一个等差数列的前4项是a，x，b,2x，则等于( )
b1112A.B.C.D. 4233【答案】C
2.已知等差数列{an}的公差为d(d≠0)，且a3＋a6＋a10＋a13＝32，若am＝8，则m为( ) A．12 B．8 C．6 D．4
1
that deal in data, the oil of the digital age. The most valuable firms are Google,Amazon,这个问题由于涉及到老牛和小马的驮包裹的两个未知数，我们设老牛驮个包裹对宇宙未来的预言，其关键问题在于宇宙的平均密度是多少。Sport is not only physically challenging, but it can also be mentally精神上地) challenging. Criticism from coaches and other teammates, as well as pressure to win can create a great amount of stress for young athletes.【答案】B
3.设等差数列A．
的公差为d，若数列
C．
为递减数列，则（ ） D．
B．
【答案】C
4. 已知{an}是等差数列，且a1＋a2＋a3＝12，a8＝16. (1)求数列{an}的通项公式；
(2)若从数列{an}中，依次取出第2项，第4项，第6项，…，第2n项，按原来顺序组成一个新数列{bn}，试求出{bn}的通项公式．
【答案】(1)an＝2n; (2) bn=4n
【解析】解： (1)∵a1＋a2＋a3＝12，∴a2＝4，
∵a8＝a2＋(8－2)d，∴16＝4＋6d，∴d＝2， ∴an＝a2＋(n－2)d＝4＋(n－2)×2＝2n.
(2)a2＝4，a4＝8，a8＝16，…，a2n＝2×2n＝4n. 当n＞1时，a2n－a2(n－1)＝4n－4(n－1)＝4. ∴{bn}是以4为首项，4为公差的等差数列． ∴bn＝b1＋(n－1)d＝4＋4(n－1)＝4n.
2
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