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# Core Maths 4: Trig identity using double angle formulae Tweet

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1. Core Maths 4: Trig identity using double angle formulae
Hi there

Many thanks
Jackie
2. Re: Core Maths 4: Trig identity using double angle formulae
You started off fine with .

Now just substitute for the and it's finished.
3. Re: Core Maths 4: Trig identity using double angle formulae
Look at the question. Then look at what you have under 8a) on the first page.
4. Re: Core Maths 4: Trig identity using double angle formulae
cos4 theta = cos squared 2 theta - sin squared 2 theta
change the sin squared 2 theta to 1 - cos squared 2 theta
now simplify and you get the answer
5. Re: Core Maths 4: Trig identity using double angle formulae
... You are aware that right?
6. Re: Core Maths 4: Trig identity using double angle formulae
(Original post by Lord of the Flies)
... You are aware that right?
Nope, but I am now
7. Re: Core Maths 4: Trig identity using double angle formulae
OK thank you all!!!