We define a recursive sequence of natural numbers such that a 1 = 2 and a n + 1 = 3 a n + 2 for n ≥ 1 . Find a 1 0 0 [ 2 ∑ n = 1 1 0 0 a n ] + 2 0 0 .
The problem is original.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Great usage of the recurrence relation.
I would expect that most people tried to solve the recurrence, and substituted those values instead.
good work, a small typo in the third last step it is 2 S + 2 0 0
a n + 1 = 3 a n + 2
a n + 1 + 1 = 3 a n + 3 = 3 ( a n + 1 )
Let b n = a n + 1 then b n + 1 = 3 b n and b 1 = 3 so b n = 3 n
Now we see a n = 3 n − 1
3 1 0 0 − 1 [ 2 n = 1 ∑ 1 0 0 ( 3 n − 1 ) ] + 2 0 0 = 3 1 0 0 − 1 [ 2 2 3 ( 3 1 0 0 − 1 ) − 2 0 0 ] + 2 0 0 = 3
nice approach
Problem Loading...
Note Loading...
Set Loading...
a n + 1 = 3 a n + 2
∑ i = 1 n a i + 1 = 3 ∑ i = 1 n a i + 2 n
a n + 1 + ∑ i = 1 n a i − a 1 = 3 ∑ i = 1 n a i + 2 n
Let S = ∑ i = 1 1 0 0 a i and substitute n = 1 0 0 .
So, a 1 0 1 + S − a 1 = 3 S + 2 0 0
3 a 1 0 0 + 2 − 2 = 2 S + 2 0 0
2 S + 2 0 0 = 3 a 1 0 0
Therefore, a 1 0 0 2 ∑ i = 1 n a i + 2 0 0 = 3