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R ADDITION FORMULAS?! Please help!!

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    Hey can someone explain how to use r addition formulas to me?

    Say they give you 2sinx + 5cosx how do you expand it and what formula do you use? In the book I'm using it says Rsinxcosa + Rcosxsina.... But I have no idea how this comes about ?!

    Someone please help my exams in 7 days!!
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    The formula comes from asinφ +/- bcosφ = Rsin(φ+α)
    It has just been expanded using the addition formulas - these are a couple of pages back if you have the same book I do
    You'll usually be told which to use .. Give your answer in the form Rsin.. And Rcos...
    If not, just go with whichever comes first
    For example with yours, use the sin formula as sin is first in the equation
    I'm doin C4 next week and don't remember ever getting a question where you had to use the R addition formulas without being told to or how to leave your answer

    Hope this helps and good luck!

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Updated: June 12, 2012
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