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Math Help - Sum and Didderence Identities w/Pictures

  1. #1
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    Sum and Didderence Identities w/Pictures

    I know the identities by hard. My problem is when its in fraction form with a radical. When do you multiply by conjugate and when not? (See picture for problem with tangent)

    Second problem I tried to use sine of sum identity (picture with words)
    Attached Thumbnails Attached Thumbnails Sum and Didderence Identities w/Pictures-trig1.jpg   Sum and Didderence Identities w/Pictures-trig2.jpg  
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  2. #2
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    Re: Sum and Didderence Identities w/Pictures

    tan 195 = tan ( 180 + 15) = tan 15
    use tan 15= tan(45-30)
    and get ur answer....
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  3. #3
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    Re: Sum and Didderence Identities w/Pictures

    sin(A+B)=sinA cosB +cosA sinB

    sin A= 3/5
    sin B =5/13
    as A is in second quadrant
    therefore cos will be negative
    cos A = -4/5
    cos B =12/13
    can u find sin (A+B) now?
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  4. #4
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    Re: Sum and Didderence Identities w/Pictures

    Sum and Didderence Identities w/Pictures-30-jun-13.png
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  5. #5
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    Re: Sum and Didderence Identities w/Pictures

    Quote Originally Posted by mpx86 View Post
    sin(A+B)=sinA cosB +cosA sinB sin A= 3/5 sin B =5/13 as A is in second quadrant therefore cos will be negative cos A = -4/5 cos B =12/13 can u find sin (A+B) now?
    How did you get -4/5 and 12/13 for cosines? Cos A= -4/5 shouldnt you apply even/odd properties?
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  6. #6
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    Re: Sum and Didderence Identities w/Pictures

    You probably used the Sine pythag identity
    Attached Thumbnails Attached Thumbnails Sum and Didderence Identities w/Pictures-solutions.jpg  
    Last edited by Melcarthus; June 30th 2013 at 09:10 AM.
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  7. #7
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    Re: Sum and Didderence Identities w/Pictures

    I got it now thanks.
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