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# need some someone to exaplain a C3 query for me watch

1. Right you know the addition formulaes; e.g. sin (A+B)
I have the solutions to a question but just don't understand one thing.

Do you know how I can get from 'cosxcos30 + sinxsin30' to:

sinxcos60 + cosxsin60
2. anyone?
3. cosxcos30+sinxsin30=cos(x-30)
sinxcos60+cosxsin60=sin(x+60)

cosx = sin(x-90)

so cos(x-30+90)=sin(x+60) = sinxcos60+cosxsin60 from above

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Updated: January 19, 2010
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