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Homework Help: Making theta the subject

  1. Nov 2, 2008 #1
    hi. with It = Io sin^2 x (4 x theta) x sin^2 (pi x dn x p / lambda) what would the equation be for making theta the subject? thanks for your input
  2. jcsd
  3. Nov 2, 2008 #2


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    What are you trying to express? It=Iosin2(4[tex]\theta[/tex]sin2([tex]\pi[/tex]dnp/[tex]\lambda[/tex])

    Maybe some of that needs to be amended as
    [tex]\frac{\pi dnp}{\lambda}[/tex]
    The typesetting tools available in the Compose for replying are new to me.

    I know that did not work, I still have trouble with these typesetting features.
    Last edited by a moderator: Nov 2, 2008
  4. Nov 2, 2008 #3


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    questions_uk, start by "reversing" what is there, just like solving any equation. Everything except [itex]sin^2(4\theta)[/itex] is a constanat so just divide both sides by [itex]Io sin^2(\pi dn p/\lambda[/itex] to get
    [tex]sin^2(4\theta)= \frac{It}{Iosin^2(\pi dn p/\lambda)}[/tex]
    Get rid of the "2" by doing the opposite: square root
    [tex]sin(4\theta)= \sqrt{\frac{It}{Iosin^2(\pi dn p/\lambda)}[/tex]
    and get rid of the sin by using arcsin:
    [tex]4\theta= arcsin\left(\sqrt{\frac{It}{Iosin^2(\pi dn p/\lambda}\right)[/tex]
    Finally, of course, divide both sides by 4.

    Since squaring and sine are not "one-to-one" functions, you might need to think about other possible values.

    Symbolipoint, use "\", not "/" inside LaTex. And I recommend that you put entire equations in LaTex, not just individual symbols. In the second one here, you had a "tex", "/tex" pair inside another!
    Last edited by a moderator: Nov 3, 2008
  5. Nov 3, 2008 #4
    hi, thanks for the reply. where did the In bit come from?
  6. Nov 3, 2008 #5


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    Sorry, that was supposed to be your It.

    I have gone back and editted to change In to It.
  7. Nov 4, 2008 #6
    Thank you for your help.
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