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    Exercise 7d question 4a?
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    Are you familiar with writing trig expressions in the form R\sin(\theta + \alpha)?
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    This is where i have got up to
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    (Original post by JSM1)
    Exercise 7d question 4a?
    How far have you got?

    Looks pretty standard to me.
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    (Original post by Muttley79)
    How far have you got?

    Looks pretty standard to me.
    ^^^^^^
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    (Original post by JSM1)
    This is where i have got up to
    OK now substitute in the values of cos and sin.

    The usual approach is to start with the LHS and compare it with Rsin (theta + alpha) - see the examples just before the exercise.
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    (Original post by Muttley79)
    OK now substitute in the values of cos and sin.

    The usual approach is to start with the LHS and compare it with Rsin (theta + alpha) - see the examples just before the exercise.
    sub in what? wheres the cos and sin?
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    (Original post by JSM1)
    This is where i have got up to
    Show that \sqrt 2 \sin\theta \cos \frac \pi 4 = \sin\theta, and similarly for the \cos term.
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    (Original post by _gcx)
    Show that \sqrt 2 \sin\theta \cos \frac \pi 4 = \sin\theta, and similarly for the \cos term.
    how?
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    (Original post by JSM1)
    how?
    What does \cos \frac \pi 4 equal?
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    (Original post by _gcx)
    What does \cos \frac \pi 4 equal?
    i dont know
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    (Original post by JSM1)
    i dont know
    Are you familiar with working with radians? If not, I'd recommend reviewing them for this topic. (pretty sure it's covered in C2 though?)
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    (Original post by _gcx)
    Are you familiar with working with radians? If not, I'd recommend reviewing them for this topic. (pretty sure it's covered in C2 though?)
    what do you do to work what it equals to?
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    (Original post by _gcx)
    Are you familiar with working with radians? If not, I'd recommend reviewing them for this topic. (pretty sure it's covered in C2 though?)
    what do you have to do?
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    (Original post by JSM1)
    what do you have to do?
    You should know the exact value of sin and cos (pi/4).

    [Hint - in degrees it would be 45]
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    (Original post by Muttley79)
    You should know the exact value of sin and cos (pi/4).

    [Hint - in degrees it would be 45]
    yes 45 degrees, then what? ms shows 1/root2. how did they get that?
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    (Original post by JSM1)
    yes 45 degrees, then what? ms shows 1/root2. how did they get that?
    You should be familiar with \sin 45^\circ = \frac 1 {\sqrt 2} at least.
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    I tend to remember these two useful triangles:

    http://edtech2.boisestate.edu/smithm...functions4.jpg

    (Source: http://edtech2.boisestate.edu/smithm...nslesson2.html ).
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    is this all you really need to know?
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    (Original post by JSM1)
    is this all you really need to know?
    It is something you need to know as well.

    The triangles are a helpful way of remembering SOME of the values of sin, cos and tan.

    In this case, we see that  \sin( \pi / 4) = \cos( \pi / 4) = \sqrt{2} / 2 = 1 / \sqrt{2}.

    This should be enough for you to complete your method of answering the question.

    ----------------------------------------------------------------------------------------------------

    You could also start using the LHS (left-hand-side) using the  R \cos (\theta \pm \alpha) method.

    This website explains this method whcih is comes up frequently in A-level:

    http://www.mathcentre.ac.uk/resource...pha-2009-1.pdf
 
 
 
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