(Ⅰ)求数列{an},{bn}的通项an和bn;
(Ⅱ)记Sn=a1b1+a2b2+…+anbn,求满足Sn<167的最大正整数n.
(Ⅰ)求数列{an},{bn}的通项an和bn;
(Ⅱ)记Sn=a1b1+a2b2+…+anbn,求满足Sn<167的最大正整数n.
解:(Ⅰ)∵Sn=2an-2,Sn-1=2an-1-2,
又Sn-Sn-1=an(n≥2,n∈N*)
∴an=2an-2an-1,∵an≠0
∴=2(n≥2,n∈N*),即数列{an}是等比数列.
∵a1=S1,∴a1=2a1-2,即a1=2.∴an=2n
∵点P(bn,bn+1)在直线x-y+2=0上,∴bn-bn+1+2=0
∴bn+1-bn=2,即数列{bn}是等差数列,
又b1=1,∴bn=2n-1
(Ⅱ)Sn=a1b1+a2b2+…anbn=1×2+3×22+5×23+…+(2n-1)2n,
∴2Sn=1×22+3×23+…+(2n-3)2n+(2n-1)2n+1
因此:
-Sn=1×2+(2×22+2×23+…+2×2n)-(2n-1)2n+1
即:-Sn=1×2+(23+24+…+2n+1)-(2n-1)2n+1
∴Sn=(2n-3)2n+2+6(10分)
∵Sn<167,即:(2n-3)·2n+1+6<167,
于是(2n-3)·2n+1<161
又由于当n=4时(2n-3)·2n+1=(2×4-3)·25=160,
当n=5时(2n-3)·2n+1=(2×5-3)·26=448,故满足条件Sn<167的最大正整数n为4