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# Some simple trig watch

1. Ok, I am going bonkers here. This should be really easy! But it's not making sense.

given

and

find

using the double angle formulae, I get

But these don't seem to convert back to the correct angles?

I seem to have confused myself. Can someone check my answers please?
2. I presume the last one is a typo, and that's meant to be root(6), not root(26).

3. (Original post by ghostwalker)
I presume the last one is a typo, and that's meant to be root(6), not root(26).

ah... yes indeed it is. not

But they don't seem to produce the right angles, do they? (when arcsin-ed etc)

Maybe they do. Can't think now. It's too late. I'll have another look tomorrow.

Thanks anyway.
4. (Original post by Plato's Trousers)
...
The way I'd check would be to find from your initial value of and then evaluate the three functions; don't attempt to do inverse trig. on them.

If you really want to take inverse trig functions of the three, then you need to be careful of which quadrant they are refering to.
5. (Original post by ghostwalker)
The way I'd check would be to find from your initial value of and then evaluate the three functions; don't attempt to do inverse trig. on them.

If you really want to take inverse trig functions of the three, then you need to be careful of which quadrant they are refering to.
yes, it actually all works out fine. Not quite sure why I couldn't do this yesterday. It's very elementary stuff.

Thanks

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Updated: March 24, 2011
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