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Is the identity sinA + sinB in C3 edecel syllabus? watch

1. Just attempting a solomon paper and came across this identity which we have never been taught, is this identity in the syllabus if so do we need to now where it comes from.
2. (Original post by alithegreat)
Just attempting a solomon paper and came across this identity which we have never been taught, is this identity in the syllabus if so do we need to now where it comes from.
Yes. This formula, and similar formulae are known as sum-product formulae, and all are in the Edexcel formula booklet.
3. (Original post by GHOSH-5)
Yes. This formula, and similar formulae are known as sum-product formulae, and all are in the Edexcel formula booklet.
Thats strange, I cant fins this identity in the book
4. (Original post by alithegreat)
Thats strange, I cant fins this identity in the book
Don't fret, it's in the formula booklet! It hardly ever comes up anyways but it is still good to know!!
5. You may get asked in the exam to prove that identity.
6. I thought that this topic was not in the syllabus, but it!

Learn it well. You never know what those naughty examiners may have up their sleeves -_-
7. Just because something is in a formula booklet does not mean that it must be in the syllabus.

I have seen formula booklets that have stuff that is definitely not in the syllabus.

Do they print different formula booklets for C1, C2, C3, C4, S1, S2, M1, M2 etc?
8. it's in the text book, chapter 7, near the end. [that is if you use the Pearson Company C3 book)
it's quite simple, do a couple of questions on it and you should be fine.
9. (Original post by alithegreat)
Just attempting a solomon paper and came across this identity which we have never been taught, is this identity in the syllabus if so do we need to now where it comes from.
It is in the book!!! They just write it as sinP + sinQ, its at the end of chapter 7.
10. (Original post by stevencarrwork)
Just because something is in a formula booklet does not mean that it must be in the syllabus.

I have seen formula booklets that have stuff that is definitely not in the syllabus.

Do they print different formula booklets for C1, C2, C3, C4, S1, S2, M1, M2 etc?
chances are that it is.
like what?

they have one formula booklet, with a page for C1,C2,C3,C4, S1, S2, M1, M2 etc.
11. Is this the thing : sin P + sin Q = 2sin (P+Q/2)cos(P-Q/2) ? If you are using the edexcel C3 book its at the end of chapter 7 , and pages 125-126 show how you can derive it and how its used.. our teacher said they only usually ask you to proove it !!
12. i dont know where this rumours came up from that it isnt in the syllabus. well the formula is in both the formula booklets: green and pink and in the text book too.

it hasnt been asked for quite some time so dont be surprised if it does come up tomorrow
13. I've never seen this in any papers, and we use the oxford book rather than the edexcel one. I've seen a proof of the cos(A)+cos(B) formula, but not the sin one. Can someone show me a proof, and also is there anything else I need to know about it?
14. (Original post by timsquirrell)
I've never seen this in any papers, and we use the oxford book rather than the edexcel one. I've seen a proof of the cos(A)+cos(B) formula, but not the sin one. Can someone show me a proof, and also is there anything else I need to know about it?

it's very similar to the cosA+cosB one.
Simply add sin(A+B) and sin(A-B) together, where you get 2sinAcosB and then let P+Q=A and P-Q=B
then 2A=P+Q and 2B=P-Q
rearranging to get A=(P+Q)/2 and B=(P-Q)/2
Which you then sub into 2sinAcosB.

EDIT: by the way, this is for sinP+sinQ [hence the P and Q]
15. That's great, thankyou! Is there anything else I need to be able to do with these, or is that all?
16. (Original post by timsquirrell)
That's great, thankyou! Is there anything else I need to be able to do with these, or is that all?
You might have to prove the differences of the sines/cosines as well. which for sine would be: sin(A+B)-sin(A-B) and for cosine would be: cos(A+B)-cos(A-B)

You have to be able to use them...(the examples I'm giving you are the ones my teacher gave us)

Stuff like simplify: sin30+sin50 (just sub the numbers in!)
which is really easy, and therefore least likely to come up.

or you could get something like:
Express -2sin4xsinx as the difference of 2 cosines

let cosP-cosQ= -2sinx4sinx

P+Q=2(4x)

P-Q=2(x)

Simultaneous equations, giving P=5x and Q=3x

therefore, cos5x-cos3x = -2sin4xsinx

or:

Solve cos4x=cos2x for 0<= x<= 180

cos4x-cos2x=0
sub into -2sin((P+Q)/2)sin((P-Q)/2)

getting: -2sin3xsinx=0

sin3x=0 and sinx=0

solve as normal.

and that was it! As you can see, it's pretty simple stuff. The hardest question related to this that I have done was on Solomon Paper G Q2(b). Give it a try if you want! [it's oddly easy once you know what to do, though]
17. It's so amazing how I practised from that C3 Book yet I never noticed those 'factor formulae' until now >_<
18. (Original post by Doughboy)
It's so amazing how I practised from that C3 Book yet I never noticed those 'factor formulae' until now >_<
I doubt that they'd turn up or that if they do, the question would be difficult!
19. They're useful to know when integrating products of sin and cos. Eg,
20. You won't be expected to memorise it, if it did ever come up it'd be a long question lots of "show that's". You'd only ever be expected to "bring it in yourself" in STEP/AEA exams

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