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Math Help - Sequences and Series. AQA C2 Pg.175 Q6.b) Find the sum of the first terms of the.....

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    Sequences and Series. AQA C2 Pg.175 Q6.b) Find the sum of the first terms of the.....

    6. An arithmetic series has sixth term 28 and tenth term 44.
    a) Find the first term and the common difference.
    U6 = a + (6-1)d, 28 = a +5d---(1)
    U10 = a + (10-1)d, 44 = a + 9d---(2)

    (1) - (2)

    16 = 4d
    d = 4
    a = 15 - 5 * 4
    a = 8

    b.Find the sum of the first terms of the series.
    ?????

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    Quote Originally Posted by ansonbound View Post
    6. An arithmetic series has sixth term 28 and tenth term 44.
    a) Find the first term and the common difference.
    U6 = a + (6-1)d, 28 = a +5d---(1)
    U10 = a + (10-1)d, 44 = a + 9d---(2)

    (1) - (2)

    16 = 4d
    d = 4
    a = 15 - 5 * 4
    a = 8

    b.Find the sum of the first terms of the series.
    ?????

    Hi ansonbound,

    How many terms do you want to find the sum of?

    Where do you want to start a_1), and where do you want to end (a_n)


    The sum of an arithmetic series is

    S_n=\frac{n}{2}(a_1+a_n)

    Just fill in what you know and solve for the sum.
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    The answer at the back of the book is 5300.??
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    Quote Originally Posted by ansonbound View Post
    The answer at the back of the book is 5300.??
    Your question says

    b) Find the sum of the first terms of the series.

    My question is 'find the sum of the first how many terms', the first 100, first 1000, what??
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