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How to use the factor formuale for integration ? Watch

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    Hello there, someone said that instead of using the addition formuale , you could use the factor formulae (P+Q) to make integration easier to do...but i dont know how to do this and is currently struggling with it...pls help me do this example:


    THANKS in advance !


    2sin2xsin5x
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    (Original post by laurawoods)
    Hello there, someone said that instead of using the addition formuale , you could use the factor formulae (P+Q) to make integration easier to do...but i dont know how to do this and is currently struggling with it...pls help me do this example:


    THANKS in advance !


    2sin2xsin5x
    To be honest using integration by parts is the best method of solving these problems.
    Learning all the Formulae is a lot of effort but and proving them is even more.
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    (Original post by laurawoods)

    2sin2xsin5x
    \cos B - \cos A =2 \sin \dfrac{A+B}{2}  \sin \dfrac{A-B}{2}

    is given in the formula booklet
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    (Original post by TenOfThem)
    \cos B - \cos A =2 \sin \dfrac{A+B}{2}  \sin \dfrac{A-B}{2}

    is given in the formula booklet
    hello there pls can u talk in terms of P and Q since that is the way it is laid out in the formula sheets and hence i would find that way easier....
    cheerios!
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    (Original post by laurawoods)
    hello there pls can u talk in terms of P and Q since that is the way it is laid out in the formula sheets and hence i would find that way easier....
    cheerios!
    I thought you did edexcel
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    (Original post by TenOfThem)
    I thought you did edexcel
    yes of course I do edexcel, sorry noticed now in the formuale sheet that it is in terms of A and B but in the TEXTBOOK in terms of P and Q,,pls can u do P and Q ...sorry for rude lang...
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    (Original post by laurawoods)
    yes of course I do edexcel!
    Then, what are you talking about re P and Q?
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    (Original post by laurawoods)
    yes of course I do edexcel, sorry noticed now in the formuale sheet that it is in terms of A and B but in the TEXTBOOK in terms of P and Q,,pls can u do P and Q ...sorry for rude lang...
    So, given that you are going to be using the formula book in the exam ... use the formula that you will get there
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    If you're not going to be bothered to learn how to apply the formulas in your formula packet, you might as well ignore them.

    But anyways:

    Let P=(A+B)/2 and Q=(A-B)/2

    Find A and B, and your formula for 2sinPsinQ will come out.
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    (Original post by aznkid66)
    If you're not going to be bothered to learn how to apply the formulas in your formula packet, you might as well ignore them.

    But anyways:

    Let P=(A+B)/2 and Q=(A-B)/2

    Find A and B, and your formula for 2sinPsinQ will come out.
    hello do what do we do after this stage:
    A+B/ 2 = 5
    A-B / 2 = 2

    Therefore adding together gives, A= 7 and B= 3

    then cos7x-cos3x ....BUT THEN WHAT I AM REALLY STUCK WITH IS HOW TO ADJUST THE CONSTANTS IN FRONT....
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    (Original post by laurawoods)
    hello do what do we do after this stage:
    A+B/ 2 = 5
    A-B / 2 = 2

    Therefore adding together gives, A= 7 and B= 3

    then cos7x-cos3x ....BUT THEN WHAT I AM REALLY STUCK WITH IS HOW TO ADJUST THE CONSTANTS IN FRONT....
    Are you saying that you do not know that

    \int \cos kx dx = \frac{1}{k}\sin kx
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    (Original post by TenOfThem)
    Are you saying that you do not know that

    \int \cos kx dx = -\frac{1}{k}\sin kx
    btw , you have got that wrong...no minus sign

    and i am not talking about that
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    (Original post by TenOfThem)
    Are you saying that you do not know that

    \int \cos kx dx = -\frac{1}{k}\sin kx
    on here we have got

    2sin2xsin5x
    what do we have to do with the two>
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    (Original post by laurawoods)
    btw , you have got that wrong...no minus sign
    good spot

    and i am not talking about that
    So, what are you talking about
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    (Original post by laurawoods)
    on here we have got

    2sin2xsin5x
    what do we have to do with the two>
    You have used the 2 already

    If you hadn't then you would just have a 2*the answer
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    (Original post by TenOfThem)
    You have used the 2 already

    If you hadn't then you would just have a 2*the answer
    how do u say that i ave used the 2 already>>>
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    (Original post by laurawoods)
    how do u say that i ave used the 2 already>>>
    Go back over your work ... you must have used the 2 ... it is in the formula
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    (Original post by TenOfThem)
    Go back over your work ... you must have used the 2 ... it is in the formula
    but isnt there a MINUS sign in the formula?
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    (Original post by laurawoods)
    but isnt there a MINUS sign in the formula?
    yes, there are a few (2 or 3 depending on how you write it)

    which one in particular are you worried about
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    (Original post by TenOfThem)
    yes, there are a few (2 or 3 depending on how you write it)

    which one in particular are you worried about
    Hello there,

    So for example when u do a question like

    integrating :

    sin6xsin2x

    there is a MINUS sign and a 2 which is coming as extra ...so what do we do?
 
 
 
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