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Math Help - Is there a way. Arithmetic Progressions. Again

  1. #1
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    Question Is there a way. Arithmetic Progressions. Again

    I need help again. I'm stuck on something.

    If, in an Arithmetic Progression, U5 (5 term) =-.05 and the sum of the first 7 terms = 21, how can we find the first term?
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  2. #2
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    e^(i*pi)'s Avatar
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    Nth term: U_n = a+(n-1)d

    Sum of n terms: S_n = \dfrac{n}{2}(2a+(n-1)d)

    Plug in what you know and solve for a
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