(Ⅰ)设等差数列{an}的公差为d,由题意,得a1+d=84a1+6d=40,解得a1=4d=4,∴an=4n;∵Tn-2bn+3=0,∴当n≥2时,Tn-1-2bn-1+3=0,两式相减,得bn=2bn-1,(n≥2)又当n=1时,b1=3,则数列{bn}为等比数列,∴bn...(Ⅰ)运用等差数列的通项公式与求和公式,根据条件列方程,求出首项和公差,得到...
试题解析:(Ⅰ)设等差数列{an}的公差为d,由题意,得 a1+d=8 4a1+6d=40 ,解得 a1=4 d=4 ,∴an=4n;∵Tn-2bn+3=0,∴当n≥2时,Tn-1-2bn-1+3=0,两式相减,得bn=2bn-1,(n≥2)又当n=1时,b1=3,则数列{bn}为等比数列,∴bn=3•2n-1; (Ⅱ) cn= 4n n为奇数 3•2n-1 n...
观察数组:(-1,1,-1),(1,2,2),(3,4,12),(5,8,40),…,(an,bn,cn),则Cn的值不可能为( ) A. 112 B. 278 C
∴an=-46+(n-1)×4=4n-50,则bn=n(an+40)=n(4n-50+40)=4n2-10n.∵bn+1-bn=4(n+1)2-10(n+1)-4n2+10n=8n-6≥8×1-6=2>0.故数列{bn}是递增数列. 点评:本题考查了等差数列的通项公式和等差数列的性质,训练了等差数列前n项和最大值的求法,考查了数列的函数特性,是中低档题....
（Ⅰ）设等差数列{an}的公差为d，由题意，得a1+d＝84a1+6d＝40，解得a1＝4d＝4，∴an=4n；∵Tn-2bn+3=0，∴当n≥2时，Tn-1-2bn-1+3=0，两式相减，得bn=2bn-1，（n≥2）又当n=1时，b1=3，则数列{bn}为等比数列，∴bn＝3?2n?1； （Ⅱ）cn＝4n n为奇数3?2n?1...
将一块钠放置在空气中最终会变成NaOH D. 钠钾的合金于室温下呈液态,可作原子反应堆的导热剂 **答案**: C **分析**:解析:若将一块钠放置于空气中,钠最终变为Na2CO3。 答案:C ©2024 Baidu |由 百度智能云 提供计算服务...
11.下图中AN 、BN属于两条相对的经线,N为北极,BC处于昼半球,C地纬度是66.5°,图中数据为纬度。 据图可知,此时(A)0° 20° 40° 60° 80° 8
The article reports that on June 11, 2005 the G8 countries agreed to cancel 100% of debts owed to multilateral institutions by 18 of the world's poorest countries, 14 of which are in Africa. The total debt owed by the 18 amounted to U.S.$40bn. Under the terms of the deal, struck...
解答解:(1)由a2a3=40,a1+a4=13,d>0. 可得{(a1+d)(a1+2d)=402a1+3d=13{(a1+d)(a1+2d)=402a1+3d=13,解得{a1=2d=3a1=2d=3, ∴an=2+3(n-1)=3n-1. ∵公比为q(0<q<1)的等比数列{bn}中,b1,b3,b5∈{160160,132132,120120,1818,1212}. ...
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