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Math Help - Assistance needed on this question!

  1. #1
    Newbie
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    Apr 2012
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    London
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    Assistance needed on this question!

    hi there,

    I'm stuck on this particular question, any help would be much appreciated.

    I need to plot 3sinwt + 4coswt to determine the resulting wave form. I then need to verify this using trigonometric formulae.

    problem is I have no idea where to start! any help would be greatly appreciated.

    Many Thanks

    MrMagoo
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  2. #2
    Senior Member
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    Mar 2012
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    Sheffield England
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    Re: Assistance needed on this question!

    Let 3sinwt+4coswt=Rsin (wt+a) for all values of t

    Now Rsin(wt+a)=Rsinwtcosa+Rcoswtsina For this to be identical to the original expression requires Rcosa=3 and Rsina=4

    So R^2(cos^2a+sin^2a)=9+16=25 The bracket=1 so R^2=25 and R=5 Sub back and get cosa=3/5 and sina=4/5 So a=53.1 degrees

    Hence 3sinwt+4coswt=5sin(wt+53.1) That is a single wave with amplitude 5
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