Math

A sequence is formed by adding together the corresponding terms of a geometric sequence and and an arithmetic sequence.The common ratio of the geometric sequence is 2 and the common difference of the arithmetic sequence is 2.The first term of the new sequence is 1 and the second term is 7.
Could you please help me find the third term of the new sequence.
Thank you.

asked by Piwo
  1. AS: a+2n
    GS: b*2^(n-1)

    a+b = 1
    a+2 + 2b = 7

    a + b = 1
    a + 2b = 5
    b = 4
    a = -3

    -3 + 2n: -3 -1 1 3 5
    4*2^(n-1): 4 8 16 32 64
    sum: 1 7 17 35 69

    Looks like 17

    posted by Steve

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