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    Wondering if anyone could help with this problem:

    The sum of the first and third terms of a geometric series is 150. The sum of the second and fourth terms of the series is −75.
    a) Find the first term and common ratio of the series.
    b) Find the sum to infinity of the series.

    This is from a C2 Solomon Paper and the mark scheme just confuses me.

    Thanks
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    (Original post by lindseyyy)
    Wondering if anyone could help with this problem:

    The sum of the first and third terms of a geometric series is 150. The sum of the second and fourth terms of the series is −75.
    a) Find the first term and common ratio of the series.
    b) Find the sum to infinity of the series.

    This is from a C2 Solomon Paper and the mark scheme just confuses me.

    Thanks
    So \ a + ar^2 = 150 and \ ar + ar^3 = -75
    Can you see an easy way to link these two equations?
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    Hint, as this is geometric, think of multiplication or division.
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    (Original post by joostan)
    So \ a + ar^2 = 150 and \ ar + ar^3 = -75
    Can you see an easy way to link these two equations?
    Thank you so much!
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    (Original post by lindseyyy)
    Thank you so much!
    No worries
 
 
 
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