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C2 Geometric Series

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    I found a question in this paper (I'll add the link) which I'm not really sure how to answer. It is on geometric series and is Q7. Parts a) and b) are fine but I can't get my head around how to do part c). If a is 1/2 surely r is 3/2 and there can be no clear sum to infinity? The formula only works when the mod of r is less than 1, right? Help....

    https://crashmaths.com/wp-content/up.../C2PPAQPV2.pdf
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    Apachai Hopachai can you help? i clearly cant
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    (Original post by Bulbasaur10)
    I found a question in this paper (I'll add the link) which I'm not really sure how to answer. It is on geometric series and is Q7. Parts a) and b) are fine but I can't get my head around how to do part c). If a is 1/2 surely r is 3/2 and there can be no clear sum to infinity? The formula only works when the mod of r is less than 1, right? Help....

    https://crashmaths.com/wp-content/up.../C2PPAQPV2.pdf
    the sum to infinity is -1 if you put a/( 1 - ( a + 1 ))

    so you want to make Sn < -1
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    (Original post by the bear)
    the sum to infinity is -1 if you put a/( 1 - ( a + 1 ))

    so you want to make Sn < -1
    Yeah that's what I thought but the mark scheme says 1, and -1 would not make sense considering every term in the series is positive.
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    (Original post by Bulbasaur10)
    Yeah that's what I thought but the mark scheme says 1, and -1 would not make sense considering every term in the series is positive.
    there are quite a few errors in the crashmaths papers :dontknow:
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    (Original post by the bear)
    there are quite a few errors in the crashmaths papers :dontknow:
    Ach... yeah. Thanks for warning me They seem to be pretty useful to an extent though. It probably is just an error.
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    (Original post by Bulbasaur10)
    Ach... yeah. Thanks for warning me They seem to be pretty useful to an extent though. It probably is just an error.
    the gcse papers for the new 9-1 fiasco bold new approach to exams are great.
 
 
 
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