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在数1和2之间插入n个实数,使得这n+2个数构成递增的等比数列,将这n+2个数的乘积记为An

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在数1和2之间插入n个实数,使得这n+2个数构成递增的等比数列,将这n+2个数的乘积记为An
令an=log以2为底An
(1)求数列{An}的前n项和Sn
(2)求Tn=tana2×tana4+tana2×tana6+...+tana2n×tana(2n+2)
(1)
q^(n+1) = 2
q= 2^[1/(n+1) ]
An = 1.q.q^2.(q^n)(2)
= 2.q^[(n+1)n/2]
= 2.2^(n/2)
= 2^[(n+2)/2]
an = logAn
= (n+2)/2
Sn = a1+a2+...+an
= (1/4)n(n+5)
(2)
tan(a2n).tan(a(2n+2))
=tan(n+1).tan(n+2)
= [tan(n+2) - tan(n+1)]/ tan1 - 1
Tn=tana2×tana4+tana4×tana6+...+tana2n×tana(2n+2)
= [tan(n+2) - tan2]/tan1 - n