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Math Help - Arthimetic Series 2

  1. #1
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    Exclamation Arthimetic Series 2

    1. The first three terms of an arithmetic sequence are given by x, (2x-5), 8.6.

    Determine the first term and the common difference.

    I know that d = t2 - 1 = t3 - t2

    So, (2x-5)-(x) = 8.6 - (2x-5) (Trying to solve for difference)

    x - 5 = 3.6 - 2x

    -5 = 3.6 - x

    -5-3.6 = - x

    x = 8.6

    x = d

    This is what I did and it was wrong... I'm not sure how to do this question. :/

    The answer is t1 = 6.2 d = 1.2
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  2. #2
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    Re: Arthimetic Series 2

    Your second step is wrong
    (2x-5)-(x) = 8.6 - (2x-5)
    x-5 = 8.6 - 2x +5 = 13.6 - 2x
    3x = 18.6 OR x = 6.2
    I am sure you would have got it
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  3. #3
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    Re: Arthimetic Series 2

    Mathnood
    Next time for such kind of exercises use the basic property of Arithmetic Progression wich simply states that if 3 numbers a,b,and c are consecutive terms of an A.P then the mid term b is the arithmetic mean of the two others i.e : b=1/2[a+c]
    Minoas
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  4. #4
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    Re: Arthimetic Series 2

    Thank you! I understand now!
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