Edexcel C3,C4 June 2013 Thread

OP

Original post by MathsNerd1

Remember you can express a rational number by a fraction, so you'll have a/b if it was rational and you've just got to go about proving that it isn't rational, therefore it's irrational.

I wouldn't worry too much about this as I doubt you'd ever get asked this in the exam :smile:

2 and 3 are co-prime ∴ only solution is p = q = 0 M1
but q ≠ 0 ∴ contradiction ∴ log2 3 is irrational
-----------------------------------------------------------
Not sure what co-prime means.

And would like to understand it just to be Better. As everyone is saying there is no point in doing a paper if your not going to learn from your mistakes had it not been for this question I would have been in the A/A* range on this paper.

So want to understand!!!

Reply 1782

Original post by Better

2 and 3 are co-prime ∴ only solution is p = q = 0 M1
but q ≠ 0 ∴ contradiction ∴ log2 3 is irrational
-----------------------------------------------------------
Not sure what co-prime means.

And would like to understand it just to be Better. As everyone is saying there is no point in doing a paper if your not going to learn from your mistakes had it not been for this question I would have been in the A/A* range on this paper.

So want to understand!!!

Okay well I see it as both 2 and 3 are both prime numbers that there will only ever be one solution when they equal each other and that will be 0, so I think co prime is just because they are both prime numbers really. :smile:

What else did you not get correct on this paper then?

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Reply 1783

OP

Original post by MathsNerd1

Okay well I see it as both 2 and 3 are both prime numbers that there will only ever be one solution when they equal each other and that will be 0, so I think co prime is just because they are both prime numbers really. :smile:

What else did you not get correct on this paper then?

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Just that question.

I'm marking my Jan 2007. The graph on my graphical calculator is different to their solution. It's ridiculous argh, and I thought I got above 70.

Are you able to explain:

http://www.tomred.org/uploads/7/7/8/3/778329/c3_ms_jan_2007.pdf

QUESTION 7,

The very last two questions how annoying. I didn't even know we had to be able to draw Graphs of the order 4

AND QUESTION 8
aii A and B

(edited 10 years ago)

Reply 1784

OP

What is cosy in terms of siny.

Sorry to flood the thread! Just don't have much time left before I leave.

Reply 1785

Original post by Better

Just that question.

I'm marking my Jan 2007. The graph on my graphical calculator is different to their solution. It's ridiculous argh, and I thought I got above 70.

Are you able to explain:

http://www.tomred.org/uploads/7/7/8/3/778329/c3_ms_jan_2007.pdf

QUESTION 7,

The very last two questions how annoying. I didn't even know we had to be able to draw Graphs of the order 4

AND QUESTION 8
aii A and B

Okay for question 7 I didn't really like it as in FM I have been taught what a graph to the power of 4 looks like, but I think they're going the basis that you've worked out your turning point which you could then go further to work out if its a minimum or maximum point and then draw from this knowledge, I'm not too sure what else they could use really :-/

Posted from TSR Mobile

Reply 1786

Original post by Better

What is cosy in terms of siny.

Sorry to flood the thread! Just don't have much time left before I leave.

Okay well they want you to see, which you could if you drew out the graphs for cos and sin that sin(pi/2-y) = cosy and vice versa really. I'm sure it's stated in the book somewhere :smile:

Reply 1787

Original post by Better

Hey guys! Very sunny day out there! Gonna take a break in a few hours

BUT Does anyone know how to do Solomon Press C3 Paper K Question 4 b
Markscheme here: http://www.tomred.org/uploads/7/7/8/3/778329/c3_qp_solomon_k.pdf

Can someone please explain the justifications?

(b) Use proof by contradiction to prove that log2 3 is irrational. (6)

hated that question ! loool, asked my teacher, got told that:

Rational can be expressed as a fraction

\frac{a}{b}

however irrational can not. for example

\pi

is irrational and can not be expressed as a fraction, closest you can get to the true value is

\frac{22}{7}

(accurate to 2 d.p.) same as

2^\frac{1}{2}

it is irrational

Spoiler

Reply 1788

OP

Original post by MathsNerd1

Okay well they want you to see, which you could if you drew out the graphs for cos and sin that sin(pi/2-y) = cosy and vice versa really. I'm sure it's stated in the book somewhere :smile:

In the book they state

sin(x) = cos(x - 90)

But nothing else. Just the Translation of a Curve. But I didn't know you could do -y, and I think this is something I should definitely know.

If anyone can provide proof why you can have a -VE y i.e. sin(pi/2-y) = cosy

Reply 1789

OP

Lol. Got 65/75 on Jan 2007. I am not in a good mood.

Oh well Alcohol time! It is too nice a day not to enjoy! Then I can get back to work for the next 10 days hardcore.

If anyone can help that would be much appreciated. But will reply later on or tomorrow thanks again. :smile:

Reply 1790

Original post by Better

Lol. Got 65/75 on Jan 2007. I am not in a good mood.

Oh well Alcohol time! It is too nice a day not to enjoy! Then I can get back to work for the next 10 days hardcore.

If anyone can help that would be much appreciated. But will reply later on or tomorrow thanks again. :smile:

have fun bro, you deserve it :biggrin:

Reply 1791

Original post by Better

Lol. Got 65/75 on Jan 2007. I am not in a good mood.

Oh well Alcohol time! It is too nice a day not to enjoy! Then I can get back to work for the next 10 days hardcore.

If anyone can help that would be much appreciated. But will reply later on or tomorrow thanks again. :smile:

That was 89 UMS which isn't that bad but just means there are little areas that you can improve on, I wouldn't worry that much as you've still got quite some time to improve from that score :smile:

Reply 1792

candyhearts

Posting a few questions I've got stuck on, any help would be much appreciated. For the first one, how would I find the x values for both graphs. I'm also stuck on 3b and 8b. Thanks :smile:

Original post by Better

In the book they state

sin(x) = cos(x - 90)

But nothing else. Just the Translation of a Curve. But I didn't know you could do -y, and I think this is something I should definitely know.

If anyone can provide proof why you can have a -VE y i.e. sin(pi/2-y) = cosy

If you use the compound angle formula for sin(A+B), you get:

sin(\frac{\pi}{2}-y)=sin{\frac{\pi}{2}}cosy-cos{\frac{\pi}{2}}siny=cosy-0=cosy

The same also works for

sin(\frac{\pi}{2})=cos(\frac{\pi}{2}-y)

.

Reply 1794

Original post by candyhearts

Posting a few questions I've got stuck on, any help would be much appreciated. For the first one, how would I find the x values for both graphs. I'm also stuck on 3b and 8b. Thanks :smile:

what are the answers to them? just so i can check if what i've done is right

Reply 1795

m4ths/maths247

7

Original post by Better

In the book they state

sin(x) = cos(x - 90)

But nothing else. Just the Translation of a Curve. But I didn't know you could do -y, and I think this is something I should definitely know.

If anyone can provide proof why you can have a -VE y i.e. sin(pi/2-y) = cosy

Have a go from the triangle I drew. :smile:

You can of course use the addition formulae as you have been given in a post above

Original post by candyhearts

Posting a few questions I've got stuck on, any help would be much appreciated. For the first one, how would I find the x values for both graphs. I'm also stuck on 3b and 8b. Thanks :smile:

for the first one i haven't got a clue.
for a) take e to both sides and rearrange solve for x.
b) let e^y = x then the equation becomes 3x + 5/x = 16 (multiply by x to make a quadratic and it should factorise giving you two values of y and remember x is e^y.

question 8a) work out the gradient do -1/m and sub in x and y-values given into y-y1=m(x-x1)
8b) work out gradient make it equal 0 and solve for alpha, i think?

(edited 10 years ago)

Reply 1797

BobLoblawLawBlog

16

Original post by candyhearts

Posting a few questions I've got stuck on, any help would be much appreciated. For the first one, how would I find the x values for both graphs. I'm also stuck on 3b and 8b. Thanks :smile:

For the first one, try finding y when x=0, and x when y=0, and for the modulus one, sketch the graph and then do the same thing for the two different graphs that are produced.

For 3(b), try multiplying everything by

e^x

.

Reply 1798