1-5 AADCA 6. 7.-1 9. eq \r(2)sin(eq \f(π,8)x+eq \f(π,4)) 10.
解:(1)∵a=(cosα,sinα),b=(cosβ,sinβ),
∴a-b=(cosα-cosβ,sinα-sinβ),
∵|a-b|=eq \f(2\r(5),5),
∴eq \r(cosα-cosβ2+sinα-sinβ2)=eq \f(2\r(5),5),
即2-2cos(α-β)=eq \f(4,5),∴cos(α-β)=eq \f(3,5).
(2)∵0<α
答案
1.(1)设等差数列{an}的首项为a1,公差为d.由S4=4S2,a2n=2an+1
得eq \b\lc\{(\a\vs4\al\co1(4a1+6d=8a1+4d,,a1+(2n-1)d=2a1+2(n-1)d+1,))
解得a1=1,d=2,因此an=2n-1,n∈N*.
(2)由题意知Tn=λ-eq \f(n,2n-1),所以n≥2时,bn=Tn-Tn-1=-eq \f(n,2n-1)+eq \f(n-1,2n-2)=eq \f(n-2,2n-1).
故cn=b2n=eq \f(2n-2,22n-1)=(n-1)eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(n-1),n∈N*.
所以Rn=0×eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(0)+1×eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(1)+2×eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(2)+3×eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(3)+…+(n-1)×eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(n-1),
则eq \f(1,4)Rn=0×eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(1)+1×eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(2)+2×eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(3)+…+(n-2)×eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(n-1)+(n-1)×eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(n),
两式相减得eq \f(3,4)Rn=eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(1)+eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(2)+eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(3)+…+eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(n-1)-(n-1)×eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(n)
=eq \f(\f(1,4)-\b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))\s\up12(n),1-\f(1,4))-(n-1)×eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(n)=eq \f(1,3)-eq \f(1+3n,3)
eq \b\lc\(\rc\)(\a\vs4\al\co1(\f(1,4)))
eq \s\up12(n),整理得Rn=eq \f(1,9)4-eq \f(3n+1,4n-1).
所以数列{cn}的前n项和Rn=eq \f(1,9)4-eq \f(3n+1,4n-1).
2.(1)设F(-c,0),由eq \f(c,a)=eq \f(\r(3),3),知a=eq \r(3)c.过点F且与x轴垂直的直线为x=-c,
代入椭圆的方程有eq \f((-c)2,a2)+eq \f(y2,b2)=1,解得y=±eq \f(\r(6)b,3).于是eq \f(2 \r(6)b,3)=eq \f(4 \r(3),3),解得b=eq \r(2).
又a2-c2=b2,从而a=eq \r(3),c=1,
所以所求椭圆的方程为eq \f(x2,3)+eq \f(y2,2)=1.
(2)设点C(x1,y1),D(x2,y2),由F(-1,0)得直线CD的方程为y=k(x+1).
由方程组eq \b\lc\{(\a\vs4\al\co1(y=k(x+1),,\f(x2,3)+\f(y2,2)=1,))消去y,整理得(2+3k2)x2+6k2x+3k2-6=0,
可得x1+x2=-eq \f(6k2,2+3k2),x1x2=eq \f(3k2-6,2+3k2).
因为A(-eq \r(3),0),B(eq \r(3),0),
所以eq \o(AC,\s\up6(→))·eq \o(DB,\s\up6(→))+eq \o(AD,\s\up6(→))·eq \o(CB,\s\up6(→))=(x1+eq \r(3),y1)·(eq \r(3)-x2,-y2)+(x2+eq \r(3),y2)·(eq \r(3)-x1,-y1)
=6-2x1x2-2y1y2
=6-2x1x2-2k2(x1+1)(x2+1)
=6-(2+2k2)x1x2-2k2(x1+x2)-2k2
=6+eq \f(2k2+12,2+3k2).
由已知得6+eq \f(2k2+12,2+3k2)=8,解得k=±eq \r(2).
3.解:(1)设数列{an}的公差为d,则2a1+3a2=2a1+3(a1+d)=5a1+3d=11,
2a3=a2+a6-4,即2(a1+2d)=a1+d+a1+5d-4,即2d=4,解得d=2,故a1=1,
故an=a1+(n-1)d=1+(n-1)×2=2n-1.
(2)结合(1)可得Sn=eq \f(na1+an,2)=n2,
∴bn=eq \f(1,Sn+1-1)=eq \f(1,n+12-1)=eq \f(1,n2+2n)=eq \f(1,nn+2)=
eq \f(1,2)(eq \f(1,n)-eq \f(1,n+2)),
Tn=eq \f(1,2)(eq \f(1,1)-eq \f(1,3)+eq \f(1,2)-eq \f(1,4)+eq \f(1,3)-eq \f(1,5)+…+eq \f(1,n-1)-eq \f(1,n+1)+eq \f(1,n)-eq \f(1,n+2))=eq \f(1,2)(eq \f(1,1)+eq \f(1,2)-eq \f(1,n+1)-eq \f(1,n+2))=eq \f(3,4)-eq \f(n+\f(3,2),n+1n+2)