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    • Thread Starter
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    what is
    n
    ∑ (2r+3^r)?
    r=1
    I struggled to find the sum of 3^r
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    (Original post by nathanking)
    what is
    n
    ∑ (2r+3^r)?
    r=1
    I struggled to find the sum of 3^r
    Think 'geometric series'.
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    too late
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    (Original post by TeeEm)
    too late
    I don't think I know this rule ...
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    (Original post by nathanking)
    I don't think I know this rule ...
    I see ...
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    (Original post by TeeEm)
    I see ...
    can you tell me how to do it please?
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    (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
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    (Original post by nathanking)
    what is
    n
    ∑ (2r+3^r)?
    r=1
    I struggled to find the sum of 3^r
    \displaystyle \sum_{r=1}^n a^r=a+a^2+a^3+....+a^n
 
 
 
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