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Math Help - need some help please cheers

  1. #1
    Newbie
    Joined
    Jul 2008
    Posts
    12

    need some help please cheers

    got this question:

    Pressure P and V are related by c . V cubed = c, where c is a constant.
    Determine the approximate % change in c when p is increased by 3% and v is decreased by 1.2%

    suggested answer:

    ( P = 1 ) x (V = 1 ) cubed = C (which is 100%)

    Therefore (( P + 3%) x (1 - 1.2%)) Cubed = Cn

    (1.03 x 0.988) Cubed = 1.053

    then you would take Cn from C to get the aproximate % change.

    is this right??
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  2. #2
    MHF Contributor
    Joined
    Nov 2008
    From
    France
    Posts
    1,458
    Hi

    P\:V^3 = c

    P'\:V'^3 = c' where P' = 1.03\:P and V' = 0.988\:V

    0.988\:V)^3 = c'" alt="1.03\:P\0.988\:V)^3 = c'" />

    1.03\:\:0.988^3\:P\:V^3 = c'

    0.9934\:c = c'

    \frac cc' = 0.9934 = 1-0.66/100

    The approximate % change in c is -0.66%
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