# Pure 2 maths help pleeeeeeeeeease

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#1
Im really stuck on the whole of question 4 on the jan 2000 paper
Pleeeeeeease help me
xox
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16 years ago
#2
(Original post by kindersurprise)
Im really stuck on the whole of question 4 on the jan 2000 paper
Pleeeeeeease help me
xox
Which is?
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#3
sorry,
The first part is:
f(x)=lnx and g(x)=x^2
What is fg(x) and gf(x)
xox
0
16 years ago
#4
(Original post by kindersurprise)
sorry,
The first part is:
f(x)=lnx and g(x)=x^2
What is fg(x) and gf(x)
xox
fg(x)=ln(x^2)
gf(x)=(lnx)^2
0
16 years ago
#5
(Original post by kindersurprise)
sorry,
The first part is:
f(x)=lnx and g(x)=x^2
What is fg(x) and gf(x)
xox
Might help if you write f(g(x)) and g(f(x)).

fg(x) = ln x^2
gf(x) = (ln x)^2
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#6
Thanx, i guess im out of practice lol, not been doing any work over easter
xox
0
16 years ago
#7
(Original post by kindersurprise)
sorry,
The first part is:
f(x)=lnx and g(x)=x^2
What is fg(x) and gf(x)
xox
What is fg(x):

g(x) = x^2:

fg(x) = f(x^2) = ln(x^2) = 2lnx

What is gf(x):

f(x) = lnx

gf(x) = g(lnx) = (lnx)^2
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16 years ago
#8
(Original post by Nylex)
Might help if you write f(g(x)) and g(f(x)).

fg(x) = ln x^2
gf(x) = (ln x)^2
For fg(x), wouldn't it be better to simplify further to 2lnx ?
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16 years ago
#9
(Original post by Ralfskini)
fg(x)=ln(x^2)
I think that 2lnx would be the better answer, as it goes that extra step in simplifying it.
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16 years ago
#10
(Original post by bono)
I think that 2lnx would be the better answer, as it goes that extra step in simplifying it.

Yeh, that bit is subjective.
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16 years ago
#11
(Original post by Ralfskini)
Yeh, that bit is subjective.
Sorry Ralf, just that my teacher always said to simplify lnx^n to nlnx
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16 years ago
#12
(Original post by bono)
Sorry Ralf, just that my teacher always said to simplify lnx^n to nlnx

No it's fine. Your way is probably better but the question is only going to be worth a mark anyway.
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16 years ago
#13
(Original post by Ralfskini)
No it's fine. Your way is probably better but the question is only going to be worth a mark anyway.
You'd be very suprised.

For that whole question we just did (hardly took long, true), it would probably get us 4 marks.
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#14
(Original post by bono)
You'd be very suprised.

For that whole question we just did (hardly took long, true), it would probably get us 4 marks.
Its 2 marks, but i needed to simlify to 2lnx for the next part of the qn
xox
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16 years ago
#15
(Original post by kindersurprise)
Its 2 marks, but i needed to simlify to 2lnx for the next part of the qn
xox
Really? Aaa, it's on your P2 Paper.

"but i needed to simlify to 2lnx" - Yes, I did that in my solution, have a look. 2lnx was my final answer.

On my syllabus we do it in P1. That question in P1 would probably collect me 4 marks, 3 at the very least.
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#16
(Original post by bono)
Really? Aaa, it's on your P2 Paper.
On my syllabus we do it in P1. That question in P1 would probably collect me 4 marks, 3 at the very least.
I guess its just meant to be assumed knowledge for p2, so its not worth as many marks. We didnt have es and logs on p1 tho, which incidentaly i HATE lol
xox
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