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The Edexcel C3 (14/06/12 - AM) Revision Thread

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On January 2010 paper, question 9iib), why is the range fg(x)>3 not fg(>=)3? fg(x) has the question: fg(x) = (x-1)² + 3, so would have a min at (1,3)?

Thanks

Reply 101

MuffinMonster

What happens if you give two sets of working and answer because you're not sure which one is right? Do they mark both?

Reply 102

0range

Original post by MuffinMonster

What happens if you give two sets of working and answer because you're not sure which one is right? Do they mark both?

yup

Reply 103

username533239

Original post by StraightUpG

Find in terms of pi, the solutions of the equation:

Sin(5X) + Sin(X) =0

for the x interval, 0<=(X)<pi

This is straight off a Solomon paper, and was wondering if a question like this can come up in an edexcel paper for C3 as I havent seen a question like it in any past papers.

Why do a pointless cocky solomon paper for an edexcel paper?

Reply 104

StraightUpG

Original post by siwelmail

Why do a pointless cocky solomon paper for an edexcel paper?

Pointless cocky solomon paper?

Reply 105

DH3498

Original post by 0range

yup

You do mostly, but if you're solving a trig equation, if you give more answers than there actually are, you lose the final A1 mark :frown:

Thats what it said on the Jan 2010 markscheme.

Reply 106

grazie

Original post by DH3498

On January 2010 paper, question 9iib), why is the range fg(x)>3 not fg(>=)3? fg(x) has the question: fg(x) = (x-1)² + 3, so would have a min at (1,3)?

Thanks

Your point is valid, but because g is defined as

g(x) = ln(x - 1), \ \ \ \ \ x \in \mathbb{R}, x > 1

x > 1 is the crucial part. When deriving fg(x), this translates to x > 3.

Reply 107

0range

Original post by DH3498

You do mostly, but if you're solving a trig equation, if you give more answers than there actually are, you lose the final A1 mark :frown:

Thats what it said on the Jan 2010 markscheme.

Yh I'm not completely sure about the trig questions, but it's what I did in S1 and C1

Reply 108

DH3498

Original post by 0range

Yh I'm not completely sure about the trig questions, but it's what I did in S1 and C1

Same I usually do put in extra ones if I'm not sure tbh, hmmm. When I do the newer papers (Jun 11/Jan 12) I'll have another look and see what it says on the markschemes (and the additional notes) and let you know :smile:

Reply 109

DH3498

Original post by grazie

Your point is valid, but because g is defined as

g(x) = ln(x - 1), \ \ \ \ \ x \in \mathbb{R}, x > 1

x > 1 is the crucial part. When deriving fg(x), this translates to x > 3.

Ahh, yeh I thought it was to do with that, thanks.

I always seem to get these range/domain questions wrong. What would you say is the best method to go about them, (and check them if possible)?

Cheers

Reply 110

M Kh

Original post by -James-

I thought compared to Jun 11 and Jan 12.

did you find them easy?

Not really.

Reply 111

0range

Original post by DH3498

Thank you

Reply 112

user977153

Not related to this thread but does anyone know if there's a thread for C4 edexcel?

Reply 113

0range

Original post by DoctorVertigo

Not related to this thread but does anyone know if there's a thread for C4 edexcel?

Here:

http://www.thestudentroom.co.uk/showthread.php?t=1992771

Reply 114

grazie

Original post by DH3498

I don't think the textbook gives enough emphasis on boundary conditions.

When they put a boundary condition in a function definition, in this case g is not defined when x=1, they really want you to spot it and understand its significance.

I can't offer more than that I'm afraid.

Reply 115

Vsfletcher

hi could someone help me out.
(1-tan^2 x)/(1+tan^2 x)=cos 2X apparently can anyone show me the steps to get to the answer???
thanks

Reply 116

0range

Original post by Vsfletcher

hi could someone help me out.
(1-tan^2 x)/(1+tan^2 x)=cos 2X apparently can anyone show me the steps to get to the answer???
thanks

Can't use latex to save my life so I'm gonna just try n word it out :P

tan^2(x) is equal to sin^2(x)/ cos^2(x)

once you've subbed that in you need to combine the 1 with the sin and the cos, then just divide and simplify like normal.

Try it again with what I've said and if you still don't get it I'll post a picture

(edited 11 years ago)

Reply 117

Callidus

I need 90% so bad!!! I'm going to spend the next 12 days cramming like hell, I hope it's a relatively straightforward paper :smile:

Reply 118

Callidus

Original post by Vsfletcher

hi could someone help me out.
(1-tan^2 x)/(1+tan^2 x)=cos 2X apparently can anyone show me the steps to get to the answer???
thanks

Took me a while to figure out myself.. god I hate trig identities!

1+tan^2 x = sec^2 x = 1/cos^2 x

Times the top row by the cos^2 x and you get cos^2 x(1-sin^2 x/cos^2 x)

Which gives you cos^2 x-sin^2 x = cos2x

You just have to learn all the different variations of the trig identities..

hope this helped :smile:

Reply 119

Vsfletcher

Original post by 0range