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Author Topic: P3 help :D  (Read 1127 times)

Offline thecandydoll

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P3 help :D
« on: May 17, 2011, 09:57:27 am »
I got three doubts,could y'all help me out?


Oct/Nov 2003 Q4 (ii)
May June 2004 (Q6)
Oct/Nov 2004 Q10 (ii)
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Offline thecandydoll

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Re: P3 help :D
« Reply #1 on: May 17, 2011, 12:54:13 pm »
BUMPPP
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elemis

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Re: P3 help :D
« Reply #2 on: May 17, 2011, 01:25:58 pm »
From the equation y=x we can :

Replace x in the original equation (given in the question) and solve for x.

Do the same for y, except replace with x.

You should get the coordinates of intersection as (a/4,a/4)

Input the these into dy/dx and solve :

\frac{dy}{dx}=-\frac{\sqrt{a/4}}{\sqrt{a/4}}

Simplify to -1.

Construct an equation :

y-a/4 = -1(x-a/4)

Simplify to answer in markscheme.
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elemis

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Re: P3 help :D
« Reply #3 on: May 17, 2011, 01:36:52 pm »
Split the variables :

\frac{1}{\frac{y^3+1}{3y^2}}dy=1dx

\frac{3y^2}{y^3+1}dy=1dx

\frac{1}{3}ln(y^3+1)=x+c

When y=1 and x=0, c = \frac{1}{3}ln(2)

ln(y^3+1)=3x+ln2<br /><br />ln(y^3+1)-ln2=3x

Can't you continue from here ?
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