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Math Help - Arithmetic Sequence problem

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    Arithmetic Sequence problem

    The sum of the fifth term and twice the third term of an arithmetic sequence equals the twelfth term. If the seventh term is 25, find an expression for the general term u_n
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    Quote Originally Posted by shawli View Post
    The sum of the fifth term and twice the third term of an arithmetic sequence equals the twelfth term. If the seventh term is 25, find an expression for the general term u_n
    U_5 + 2U_3 = U_{12}

    Since U_n = a + (n-1)d we can rewrite this as

    (a+4d) + (2a+4d) = a + 11d

    You can simplify that down by collecting like terms.

    U_7 = a + 6d = 25

    You know have two equations from which you can find a and d
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    Errr nevermind, I got it!

    Thanks for clicking though
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