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Math Help - geometric progression--need help 2

  1. #1
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    geometric progression--need help 2

    first term is 440 and 12th term is 880. find S6.

    so a= 12 r^11 =2 (i think some thing wrong on my calculation )

    need help
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  2. #2
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    Quote Originally Posted by nikk View Post
    first term is 440 and 12th term is 880. find S6.

    so a= 12 r^11 =2 (i think some thing wrong on my calculation )

    need help
    First term = a = 440.

    880 = a r^11 = 440 r^11 => r^11 = 2 => r = ....?

    Now substitute a, r and n (= 6) into the sum formula.
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  3. #3
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    it look like my ans up to here still correct

    First term = a = 440.

    880 = a r^11 = 440 r^11 => r^11 = 2 => r = ....?

    so..my last ans is 3108.36

    any one can reconfirm it back
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