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C3 Trig help watch

1. Can someone help me with 9i. Not sure how to do it?
Need some help starting off

http://www.ocr.org.uk/Images/144592-...hematics-3.pdf
2. (Original post by Super199)
Can someone help me with 9i. Not sure how to do it?
Need some help starting off

3. (Original post by aoxa)
Oh haha forgot to link it.
4. Wow, that's alot of work for 4 marks.

I would start off by expanding then multiplying that by itself and then cleaning up.
5. (Original post by Super199)
Oh haha forgot to link it.
You're getting the LHS to simplify down to the RHS, so it's just using all the trig identities for cos^2(theta+45) and sin/cos 2theta and manipulating the expression, then simplifying
6. I think, as there are 2thetas in there I'd look at replacing the first term by using the double angle formula in terms of cos^2 theta.
7. (Original post by aoxa)
You're getting the LHS to simplify down to the RHS, so it's just using all the trig identities for cos^2(theta+45) and sin/cos 2theta and manipulating the expression, then simplifying
When you expand cos^2(theta+45) do you have to cos(theta+45) x cos(theta+45)?
Seems a bit hefty

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