已知数列{an}满足a1=1,a(n+1)=an+√((an)^2+1),令an=tanθn(0

来源：学生作业帮助网 编辑：作业帮 时间：2024/11/24 13:02:44
已知数列{an}满足a1=1,a(n+1)=an+√((an)^2+1),令an=tanθn(0
xSKN07 X&=J$Ê(;T@VE|6 ء"nPz$1D3ޛ'a>ݏ:Wm<ސj3_$xE8b3BB%_JK5).{#m[<4d–NVm[XX3)GIU%TàV jwMgH\ td31֧PԔ!M]dynb%"~L"A$<!eszNE@f@1_0G*.nYD#<ோJ X66 #-6;ڝiT!$lM?3ۡSRX2= > f'a>R[44* i=jM)7>n|> i|;;-[M^&ϻE:Lo`ƣN|nPltҗI;l(:-v7

已知数列{an}满足a1=1,a(n+1)=an+√((an)^2+1),令an=tanθn(0
已知数列{an}满足a1=1,a(n+1)=an+√((an)^2+1),令an=tanθn(0<θn<π/2),求证(1)
已知数列{an}满足a1=1,a(n+1)=an+√((an)^2+1),令an=tanθn(0<θn<π/2),求证（1）数列{θn-π/2}是等比数列（2）a1+a2+…+an>(n-1)π/2

已知数列{an}满足a1=1,a(n+1)=an+√((an)^2+1),令an=tanθn(0
(1)
a(n+1)=an+√((an)^2+1)
a(n+1)=tan(θ(n+1))
an+√((an)^2+1)=tan(θn)+√(tan^2(θn)+1)=tan(θn)+1/(cos(θn))
=(sin(θn)+1)/(cos(θn))
=(sin(θn)+sin^2(θn/2)+cos^2(θn/2))/(cos(θn))
=(2*sin(θn/2)*cos(θn/2)+sin^2(θn/2)+cos^2(θn/2))/(cos^2(θn/2)-sin^2(θn/2))
=(sin(θn/2)+cos(θn/2))^2/((sin(θn/2)+cos(θn/2))(cos(θn/2)-sin(θn/2)))
=(sin(θn/2)+cos(θn/2))/(cos(θn/2)-sin(θn/2)))
=(tan(θn/2)+1)/(1-tan(θn/2))
=tan(θn/2+π/4)
即θ(n+1)=θn/2+π/4
θ(n+1)-π/2=(1/2)*(θn-π/2)
故{θn-π/2}是等比数列
(2)
a1=tan(θ1)=1
0<θn<π/2
θ1=π/4
θ1-π/2=-π/4
θn-π/2=-(1/2)^(n-1)*π/4=-π/(2^(n+1))
θn=π/2-π/(2^(n+1))
θ1+θ2+…+θn=n*π/2-(π/4)*(2-1/(2^(n-1)))=(n-1)*π/2+(π/4)*1/(2^(n-1))>(n-1)*π/2
由0<θn<π/2
tan(θn)>θn
a1+a2+…+an=tan(θ1)+tan(θ2)+…+tan(θn)>θ1+θ2+…+θn>(n-1)*π/2

好久没打字了，打字练习练习，速度还不错哟，

已知数列{an}满足a(n+1)=an+n,a1=1,则an= 已知数列{an}满足a(n+1)=an+lg2,a1=1,求an 已知数列{an}满足a1=1,3a(n+1)+an-7 已知数列an满足a1=1,a(n+1)=an/(3an+1) 求数列通项公式 已知数列an满足:a1=1,an-a(n-1)=n n大于等于2 求an 已知数列{an}满足a1=33,a(n+1)-an=2n,则an/n的最小值 已知数列{an}满足a1=33,a（n+1）-an=2n,求an/n的最小值 已知数列an满足a1=100,a(n+1)-an=2n,则(an)/n的最小值为 已知数列an满足a1=2,an=a(n-1)+2n,（n≥2）,求an 已知数列满足a1=1,an-a(n-1)=n-1,求其通项 已知数列｛an｝满足a1=1,a（n+1）=nan n+1是角标 已知数列{an}满足a1=2,a(n+1)-an=a(n+1）*an,则a31=? 已知数列{a}满足a1=1/2,a（n+1）=an+1/(n^2+n),求an已知数列{a}满足a1=1/2,a（n+1）=an+1/(n^2+n),求an 已知数列｛an｝满足a(n+1)=an+3n+2,且a1=2,求an=? 已知数列{an}满足a1=5,a(n+1)=an+6n+6,则an= 已知数列an满足a(n+1)=an+3n+2,且a1=2,求an 已知数列{an}满足条件a1=3,且a( n+1)-an=(20)^n+n,求通项公式已知数列{an}满足条件a1=3,且a( n+1)-an=(2)^n+n,求通项公式 已知数列an满足a1=1,a(n+1)=an/(3an+2),则an=?