求极限lim(n趋于无穷大)(a +a^2 +a^3+ ...+ a^n)/(2 +2^2+ ...+2^n)(a>0,a不等于1)

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求极限lim(n趋于无穷大)(a +a^2 +a^3+ ...+ a^n)/(2 +2^2+ ...+2^n)(a>0,a不等于1)
求极限lim(n趋于无穷大)(a +a^2 +a^3+ ...+ a^n)/(2 +2^2+ ...+2^n)(a>0,a不等于1)

求极限lim(n趋于无穷大)(a +a^2 +a^3+ ...+ a^n)/(2 +2^2+ ...+2^n)(a>0,a不等于1)
a +a^2 +a^3+ ...+ a^n = a(1 - a^n)/1-a
2 +2^2+ ...+2^n = 2(1 - 2^n)/(1 - 2) = 2^(n+1) - 2
0 < a < 1 时
lim(n趋于无穷大)(a +a^2 +a^3+ ...+ a^n)
= lim(n趋于无穷大)a(1 - a^n)/1-a
= a / 1 - a
lim(n趋于无穷大)(2 +2^2+ ...+2^n)
= lim(n趋于无穷大)2^(n+1)-2
= 无穷大
lim(n趋于无穷大)(a +a^2 +a^3+ ...+ a^n)/(2 +2^2+ ...+2^n) = 0
a > 1 时
lim(n趋于无穷大)(a +a^2 +a^3+ ...+ a^n)
= a^n
lim(n趋于无穷大)(2 +2^2+ ...+2^n)
= 2^n
lim(n趋于无穷大)(a +a^2 +a^3+ ...+ a^n)/(2 +2^2+ ...+2^n) =
= lim(n趋于无穷大)(a/2)^n
a > 2时,等于无穷大
a = 2时,等于1
1