# need some help please cheers

• Mar 13th 2009, 06:31 AM
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%

( 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??
• Mar 13th 2009, 07:37 AM
running-gag
Hi

$P\:V^3 = c$

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

$1.03\:P\:(0.988\:V)^3 = c'$

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

$0.9934\:c = c'$

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

The approximate % change in c is -0.66%