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# Pure 2 maths help pleeeeeeeeeease watch

1. Im really stuck on the whole of question 4 on the jan 2000 paper
Pleeeeeeease help me
xox
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?
3. sorry,
The first part is:
f(x)=lnx and g(x)=x^2
What is fg(x) and gf(x)
xox
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
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
6. Thanx, i guess im out of practice lol, not been doing any work over easter
xox
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
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 ?
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.
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.
11. (Original post by Ralfskini)
Yeh, that bit is subjective.
Sorry Ralf, just that my teacher always said to simplify lnx^n to nlnx
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.
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.
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
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.
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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