AQA Core 4 Exam Discussion 14/06/2012 !Poll, paper and unofficial MS (first post)!

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Can anyone give me a hand with this proof?

\dfrac{cos2x}{cosx - sinx} \ = cosx + sinx

I've put it in to the form

\dfrac{cos^2x-sin^2x}{cosx - sinx}

but don't know what to do with it next.

I get the feeling I'm missing something very obvious here - but I've done so much maths today that my brain has turned to mush!

Thanks :smile:

DOTS?

Reply 381

f1mad

Original post by musicmedic

Can anyone give me a hand with this proof?

\dfrac{cos2x}{cosx - sinx} \ = cosx + sinx

I've put it in to the form

\dfrac{cos^2x-sin^2x}{cosx - sinx}

but don't know what to do with it next.

I get the feeling I'm missing something very obvious here - but I've done so much maths today that my brain has turned to mush!

Thanks :smile:

Difference of two squares.

Reply 382

musicmedic

Original post by oli_G

DOTS?

Original post by f1mad

Difference of two squares.

Thank you both! I definitely didn't see that, but I've got it now :h:

Reply 383

vedderfan94

81 is the magic number for me (to get an A*). Good luck everyone! :smile:

Reply 384

Magickal

I really wish I didn't need 94 on this >.<

Reply 385

thedifferentiator

Somebody help thoroughly explain this type of vectors question to me please?
A(4,-3,2)

Line 1 passes through A and has equation R= (4,-3,2) + L(2,0,1)

Line 2 has equation R= (-1,3,4) + m(1,-2,-1)

B lies on line 2 where m=2

A) Find vector AB ---- (-3,2,0)
B) Show the lines intersect---- I done this and found M=3 and L=-1
ii) Lines 1 and 2 intersect at P, find P's coordinates--- P(2,-3,1)

So they are all correct I checked the mark scheme but the next question is what I need help with, I dont even know how to start and need it fully explaining, feel free to picture it and post it here

C) The point C lies on a line parallel to line 1 and which passes through the point B. A,B,C and P are the vertices of a parallelogram.

Find the possible coordinates of point C

If it makes it easier, its question 7C on june 10

Reply 386

HappyBun

Original post by lee_vassallo

Use substitution, you get 1/(1-x)

Oh thank you so much!!

Reply 387

uxa595

http://store.aqa.org.uk/qual/gce/pdf/AQA-MPC4-W-QP-JAN11.PDF
Q3c

How do you do it?

The answer is: -3/5 < x < 3/5

Reply 388

rachaelizabeth

Original post by Magickal

I really wish I didn't need 94 on this >.<

I'm in the exact same position :frown:

Good luck!

Reply 389

Cath-ay

Original post by uxa595

http://store.aqa.org.uk/qual/gce/pdf/AQA-MPC4-W-QP-JAN11.PDF
Q3c

How do you do it?

The answer is: -3/5 < x < 3/5

I explained the concept in this post:

http://www.thestudentroom.co.uk/showthread.php?t=2004642&page=15&p=38057559#post38057559

but for 3c) of a different paper. Does it help?

Reply 390

Cath-ay

Original post by rachaelizabeth

I'm in the exact same position :frown:

Good luck!

for an A*?

so far, I think there's 3 people aiming for 94 ums on this thread... Three's a crowd =]

Reply 391

Oromis263

Original post by vedderfan94

81 is the magic number for me (to get an A*). Good luck everyone! :smile:

80 is all I need as well, just hoping the vectors doesn't throw me, as I tend to take the longest route there, thus wasting a lot of time. I'm struggling to see how they can make certain topics 'hard' though. For example, the factor theorem, binomial expansion and the differential equations stuff seems to be have just one level of difficulty. Really hoping they don't give an evil question with the rest simpler, I'd prefer a more level (if perhaps, a little more difficult across the board) paper. :smile:

Reply 392

uxa595

Original post by Cath-ay

I explained the concept in this post:

http://www.thestudentroom.co.uk/showthread.php?t=2004642&page=15&p=38057559#post38057559

but for 3c) of a different paper. Does it help?

I realise that the value of the binomial has to be -1 and less then 1.

However, i still can't see why the upper boundary is 3/5 ?

Reply 393

username896004

Original post by vedderfan94

81 is the magic number for me (to get an A*). Good luck everyone! :smile:

ditto!

Reply 394

Oromis263

Original post by uxa595

I realise that the value of the binomial has to be -1 and less then 1.

However, i still can't see why the upper boundary is 3/5 ?

For a expansion:

(b+ax)^n

where b = 1, then

|x|<\dfrac{1}{a}

Is that what you need?

Reply 395

mack94

Hello i really got aproblem with differential equations

If you end up with 3=2^3x

Is it OK to take logs with base 2?

Im sure theres another way of taking ln of both sides but i dont know how!

Reply 396

Oromis263

Original post by mack94

Hello i really got aproblem with differential equations

If you end up with 3=2^3x

Is it OK to take logs with base 2?

Im sure theres another way of taking ln of both sides but i dont know how!