quine

The 2nd and 5th term of a geometric progression are - 6 & 48 find the sum of the first four term respectively

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  1. a+d = -6
    a+4d = 48
    so,
    3d=54
    d=18
    so, a=-24
    and the sequence is

    -24 -6 12 30 48 ...

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  2. I think this method is for a. P, not gp

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  3. I think this method is for a. P, not gp
    The correct one is
    ar=-6
    ar^4=48
    r^3=-8
    So r=-2
    Sn=a(1-r^n)
    - - - - - - - -
    1-r
    S4=3(1-(-2^4)
    - - - - - - - -
    1-(-2)
    S4=3(1-16)
    - - - - -
    1+2
    S4=3(-15)
    - - - - -
    3
    S4=-15
    That's the correct answer.

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