高中数学数列练习题?1.设{An}公比为q,{An +1}公比为q',则An=2*q^n-1,An +1=3*q'^n-1,1+2*q^n-1=3*q'^n-1对任意n满足,由n=2,n=3,得1+2q=3q',那么,高中数学数列练习题?一起来了解一下吧。
(1),a1=2,a2=4,a3=6,a4=8, 通项an=2n;
(2),bn=n*2^an=n*2^(2n)=n*4^n
Sn=1*4^1+2*4^2+3*4^3+……+n*4^n
4Sn=1*4^2+2*4^3+3*4^4+……+n*4^(n+1)
3Sn=4Sn-Sn
=-1*4^1+(1-2)*4^2+(2-3)*4^3+……+[(n-1)-n]*4^n+n*4^(n+1)
=-4^1-4^2-4^3-……-4^n+n*4^(n+1)
=-4*(1-4^n)/(1-4)+n*4^(n+1)
=-4^(n+1)/3+4/3+n*4^(n+1)
=(3n-1)*4^(n+1)/3+4/3
所以Sn=(3n-1)*4^(n+1)/9+4/9
(3)Y>9*Sn-3n*4^(n+1)=(3n-1)*4^(n+1)+4-3n*4^(n+1)=-4^(n+1)+4
因为n≥1
则Y>-4^(1+1)+4=-12
所以Y最小整数值为-11
a3a7=-16, a4+a6=0=a3+a7
设a3a7为方程2根
得a3=-4,a7=4
a1=-8 ,公差为2
an=-8+2(n-1)=-10+2n
Sn=n^2-9n
1.设{An}公比为q,{An
+1}公比为q',则An=2*q^n-1,An
+1=3*q'^n-1,
1+2*q^n-1=3*q'^n-1对任意n满足,
由n=2,n=3,得1+2q=3q',1+2q^2=3q'^2,解方程组得q=q'=1,
Sn=2n
2.
sn=a(1-q^n)/1-q,
p-sn=[p(1-q)-a(1-q^n)]/1-q=[p(1-q)-a+aq^n]/1-q
p-sn+1=[p(1-q)-a+aq^n+1]/1-q
(p-sn+1)/(p-sn)=1+a(q-1)q^n/[p(1-q)-a+aq^n]=c(与n无关)
则p(1-q)-a=0,即p=a/(1-q)
3.a1=1,d=2,an=2n-1,bn=(2n-1)/2^n,
tn=b1+b2+...+bn=1/2+3/4+5/8+...+(2n-3)/2^n-1
+(2n-1)/2^n
2tn=1+3/2+5/4+7/8+...+(2n-1)/2^n-1
tn=2tn-tn=1+2/2+2/4+2/8+...+2/2^n-1-
(2n-1)/2^n
=1+1[1-(1/2)^n-1]/(1-1/2)-(2n-1)/2^n
=1+2-4/2^n-(2n-1)/2^n
=3-(3+2n)/2^n
设wn=tn+
k/an+1=(k+3)/(2n+3)
-1/2^n
wn+1=tn+1
+k/an+2=(k+3)/(2n+5)
-1/2^n+1
wn+1/wn=1/2+[(k+3)/(2n+5)-1/2(k+3)/(2n+3)]/[(k+3)/(2n+3)-1/2^n]=c(与n无关),所以k+3=0,k=-3
4.由OB=A1*OA+A200*OC,(OB,OA,OC都是向量)且A,B,C三点共线(此线不过原点),
及***矢量平行四边形法则知A1+A200=1/2,所以s200=200*(A1+A200)/2=50
1.设{An}公比为q,{An
+1}公比为q',则An=2*q^n-1,An
+1=3*q'^n-1,
1+2*q^n-1=3*q'^n-1对任意n满足,
由n=2,n=3,得1+2q=3q',1+2q^2=3q'^2,解方程组得q=q'=1,
Sn=2n
2.
sn=a(1-q^n)/1-q,
p-sn=[p(1-q)-a(1-q^n)]/1-q=[p(1-q)-a+aq^n]/1-q
p-sn+1=[p(1-q)-a+aq^n+1]/1-q
(p-sn+1)/(p-sn)=1+a(q-1)q^n/[p(1-q)-a+aq^n]=c(与n无关)
则p(1-q)-a=0,即p=a/(1-q)
3.a1=1,d=2,an=2n-1,bn=(2n-1)/2^n,
tn=b1+b2+...+bn=1/2+3/4+5/8+...+(2n-3)/2^n-1
+(2n-1)/2^n
2tn=1+3/2+5/4+7/8+...+(2n-1)/2^n-1
tn=2tn-tn=1+2/2+2/4+2/8+...+2/2^n-1-
(2n-1)/2^n
=1+1[1-(1/2)^n-1]/(1-1/2)-(2n-1)/2^n
=1+2-4/2^n-(2n-1)/2^n
=3-(3+2n)/2^n
设wn=tn+
k/an+1=(k+3)/(2n+3)
-1/2^n
wn+1=tn+1
+k/an+2=(k+3)/(2n+5)
-1/2^n+1
wn+1/wn=1/2+[(k+3)/(2n+5)-1/2(k+3)/(2n+3)]/[(k+3)/(2n+3)-1/2^n]=c(与n无关),所以k+3=0,k=-3
4.由OB=A1*OA+A200*OC,(OB,OA,OC都是向量)且A,B,C三点共线(此线不过原点),
及***矢量平行四边形法则知A1+A200=1/2,所以s200=200*(A1+A200)/2=50
a4+a6=0可化成a5-d+a5+d=0;a3a7=-16可化成(a5-2d)(a5+2d)=-16可算出d=2或d=-2
然后求出两种d情况下的a1,然后用公式(a1+an)n/2
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