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Math Help - Derivee?:!

  1. #1
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    Derivee?:!

    hey all hope ur fine!!
    i need ur help :
    knowing that: cos (a+x) =cosa.cosx - sina.sin X show, by derivation that: sin (a+x) =sina.cos x+ cosa.sin X

    anny help guys?
    many thanks
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  2. #2
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    Quote Originally Posted by iceman1 View Post
    hey all hope ur fine!!
    i need ur help :
    knowing that: cos (a+x) =cosa.cosx - sina.sin X show, by derivation that: sin (a+x) =sina.cos x+ cosa.sin X

    anny help guys?
    many thanks
    Hint: sin x = cos (pi/2 -x )
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  3. #3
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    Lexington, MA (USA)
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    Hello, iceman!

    Knowing that: .cos(a + x) .= .cos(a)Ěcos(x) - sin(a)Ěsin(x)
    show by derivation that: .sin(a + x) .= .sin(a)Ěcos(x) + cos(a)Ěsin(x)
    I assume that a is a constant.

    If "by derivation" means "differentiation", the proof goes like this . . .


    Differentiate the given equation:

    . . . . . . . . . . .-sin(a + x) .= .cos(a)Ě[-sin(x)] - sin(a)Ěcos(x)

    . . . . . . . . . . .-sin(a + x) .= .-sin(a)Ěcos(x) - cos(a)Ěsin(x)


    Multiply by -1: .sin(a + x) .= .sin(a)Ěcos(x) + cos(a)Ěsin(x)

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