Turn on thread page Beta

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

    • Thread Starter
    Offline

    2
    ReputationRep:
    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.
    Offline

    12
    ReputationRep:
    (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.
    • Thread Starter
    Offline

    2
    ReputationRep:
    (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
    Offline

    14
    ReputationRep:
    (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!!
    Offline

    16
    ReputationRep:
    You may get asked in the exam to prove that identity.
    Offline

    9
    ReputationRep:
    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 -_-
    Offline

    0
    ReputationRep:
    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?
    Offline

    2
    ReputationRep:
    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.
    Offline

    14
    ReputationRep:
    (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.
    Offline

    2
    ReputationRep:
    (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.
    Offline

    0
    ReputationRep:
    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 !!
    • PS Helper
    Offline

    0
    ReputationRep:
    PS Helper
    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
    Offline

    0
    ReputationRep:
    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?
    Offline

    2
    ReputationRep:
    (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]
    Offline

    0
    ReputationRep:
    That's great, thankyou! Is there anything else I need to be able to do with these, or is that all?
    Offline

    2
    ReputationRep:
    (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]
    Offline

    9
    ReputationRep:
    It's so amazing how I practised from that C3 Book yet I never noticed those 'factor formulae' until now >_<
    Offline

    2
    ReputationRep:
    (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!
    Offline

    13
    ReputationRep:
    They're useful to know when integrating products of sin and cos. Eg, \displaystyle \int \sin{(3x)}\cos{(2x)}dx = \int \frac{\sin{(5x)}+\sin{(x)}}{2}dx
    Offline

    2
    ReputationRep:
    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
 
 
 
The home of Results and Clearing

2,875

people online now

1,567,000

students helped last year

University open days

  1. Bournemouth University
    Clearing Open Day Undergraduate
    Wed, 22 Aug '18
  2. University of Buckingham
    Postgraduate Open Evening Postgraduate
    Thu, 23 Aug '18
  3. University of Glasgow
    All Subjects Undergraduate
    Tue, 28 Aug '18
Poll
How are you feeling about GCSE results day?
Useful resources

Make your revision easier

Maths

Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

Equations

How to use LaTex

Writing equations the easy way

Student revising

Study habits of A* students

Top tips from students who have already aced their exams

Study Planner

Create your own Study Planner

Never miss a deadline again

Polling station sign

Thinking about a maths degree?

Chat with other maths applicants

Can you help? Study help unanswered threads

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.