Posted by Paul on Friday, September 21, 2012 at 12:47pm.
I was able to solve (e), this is the only one I don't get.
Determine whether the series is convergent or divergent and say what test you used to solve it.
(d) sum n=1 to infinity
(5n)^(3n) / (5^n + 3)^n

Calculus  Steve, Friday, September 21, 2012 at 3:53pm
Tn = (5n)^(3n) / (5^n + 3)^n
Tn+1 = (5(n+1))^(3(n+1)) / (5^(n+1) + 3)^(n)
Tn+1/Tn = (5(n+1))^(3(n+1)) / (5^(n+1) + 3)^(n+1) * (5^n + 3)^n / (5n)^(3n)
As n>oo, 5^n+3 is just 5^n, so we can simplify things a bit to
(5n)^(3n) * (5n)^3 * 5^(n^2)
 =
(5n)^(3n) * 5^n * 5(n^2)
(5n)^3 / 5^n
Since exponentials grow faster than powers, the ratio is less than 1, so the series converges absolutely.

Calculus  Paul, Friday, September 21, 2012 at 4:41pm
what does Tn stand for?

Calculus  Steve, Saturday, September 22, 2012 at 12:13am
nth Term of sequence
I thought it would be clear from the context and the obvious use of the ratio test.
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