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    Hi so I'm a little stuck a question to do with sine, cos and tan.

    So the question goes like this:

    If sin x = a and cos x = b:

    Find (in terms of a and b):

    1. cos(270+x)

    2. -2 tan (-x)

    3. 2 cos^2(180+x)



    I've had a go at them but I'm finding it quite confusing so it would be good if you could explain how you did it as well as stating your answer.
    Thanks!
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    Anyone?
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      (Original post by Jack_8)
      Anyone?
      For the first one: do you remember the formula to expand cos(x+y)?
      For the second one: can you write sin(-x) and cos(-x) in terms of \sin (x) and \cos (x) respectively?
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      I'm not totally sure what you mean by the formula to expand that...

      and for the second one, wouldn't sin(-x) just be -sin(x) ?
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        (Original post by Jack_8)
        I'm not totally sure what you mean by the formula to expand that...

        and for the second one, wouldn't sin(-x) just be -sin(x) ?
        Yes for the second one.

        For the first one, you should have seen a formula which is something like \cos (A+B) = \cos A \cos B - \sin A \sin B. You need to apply that. (nb. i'm not confident about my recall of that formula - it's been a long time since i've used it! - so you should look it up to check.)
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        For the first one, use Cos(A+B)=cosAcosB-SinASinB
        For the second, I used Tanx = Sinx / Cosx.
        For the 3rd one, you can use the formula from the first question,
       
       
       
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