1. ## 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%

( 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??

2. Hi

$\displaystyle P\:V^3 = c$

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

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

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

$\displaystyle 0.9934\:c = c'$

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

The approximate % change in c is -0.66%
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