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# Sine,Cos,Tan! Watch

1. 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!
2. Anyone?
3. (Original post by Jack_8)
Anyone?
For the first one: do you remember the formula to expand ?
For the second one: can you write and in terms of and respectively?
4. 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) ?
5. (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 . 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.)
6. 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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Updated: November 29, 2010
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