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# series watch

1. what is
n
∑ (2r+3^r)?
r=1
I struggled to find the sum of 3^r
2. (Original post by nathanking)
what is
n
∑ (2r+3^r)?
r=1
I struggled to find the sum of 3^r
Think 'geometric series'.
3. too late
4. (Original post by TeeEm)
too late
I don't think I know this rule ...
5. (Original post by nathanking)
I don't think I know this rule ...
I see ...
6. (Original post by TeeEm)
I see ...
can you tell me how to do it please?
7. (Original post by nathanking)
can you tell me how to do it please?
split the sum into 2
consider each sum separately
fist sum is an Arithmetic series
second sum is a geometric series
etc
8. (Original post by nathanking)
what is
n
∑ (2r+3^r)?
r=1
I struggled to find the sum of 3^r

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