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Homework Help: Finding angle X when given an inequation and a weird equation

  1. Jul 22, 2009 #1
    1. The problem statement, all variables and given/known data

    sin (x) + sin (2x) + sin (3x) = 0
    http://www4b.wolframalpha.com/Calculate/MSP/MSP531196eg6ff0edb8i9400000gb08c7ag3hfbfeh?MSPStoreType=image/gif&s=8 [Broken]

    Sorry for not following the recommended layout, it's just that this question boggles me and I don't know any relevant formulas or where to start.

    I know the http://www28.wolframalpha.com/input/?i=sin+x+++sin+2x+++sin+3x+=+0,+pi/2+<+x+<+pi"but I don't know how to get to it.

    Thanks in advance to whoever tries to help
    Last edited by a moderator: May 4, 2017
  2. jcsd
  3. Jul 22, 2009 #2


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    Homework Helper

    Do you know a formula for sinP+sinQ? (or the sum to product formula for sin?)
  4. Jul 22, 2009 #3


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    Homework Helper

    Use the double-angle formula to expand the [tex]sin(2x)[/tex] and [tex]sin(3x)[/tex] - notice that [tex]sin(3x)=sin(2x+x)[/tex] , then collect like terms and factor as much as possible while using [tex]sin^2(x)+cos^2(x)=1[/tex] to aid you in the factoring process.
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