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Homework Help: Current in circuit (trig problem)

  1. Feb 25, 2007 #1
    Hey this is my first post... been really stuck on this particular question from a paper:

    In a particular circuit the current, I amperes, is given by:

    I=4sinθ - 3cosθ θ>0

    where θ is an angle related to the voltage.

    Given that I=R x sin(θ-a), where R>0 and 0<=a<360degrees,

    a) find the value of R, and the value of a to 1 decimal place.
    b) Hence solve the equation 4sinθ - 3cosθ = 3 to find the values of θ between 0 and 360degrees.
    c) Write down the greatest value for I.
    d) Find the value of θ between 0 and 360degrees at which the greatest value of I occurs.

    I think if someone could show me the steps to answering part a) I could be able to do the rest myself.
  2. jcsd
  3. Feb 25, 2007 #2


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    Science Advisor

    [itex]Rsin(\theta- a)= Rsin(\theta)cos(a)- Rcos(\theta)sin(a)[/itex]

    Compare that with I.
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