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The 3rd and 4th term of geometric progression are 4 and 8 respectively find:
The first term and common ratio,
The sum of the first 10 term,
The sum of infinity.

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  1. Anyone to help solve this pliz

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  2. Just apply the definitions:
    3rd term = ar^2 = 4
    4th term = ar^3 = 8
    divide them
    ar^3/(ar^2) = 8/4
    r = 1/2
    back in ar^2 = 4
    a(1/4) = 4
    a = 16

    sum(10) = a(1 - r^10)/(1-r)
    = 16( 1 - 1/1024)/(1 - 1/2)
    = 16(1023/1024)(2/1) = 1023/32

    sum(all terms) = a/(1-r)
    = 16/(1/2) = 32

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