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Addition Formula/Sine Rule

  1. Apr 17, 2007 #1
    I know an alternative way of showing Sin C is cos 'theta'.
  2. jcsd
  3. Apr 17, 2007 #2
    What is angle C? I can't make it out in the picture... Also could you show your attempt of the problems?
  4. Apr 17, 2007 #3
    Angle C is pi/2 - theta (radians) "pi over two minus theta" ie. 90 deegrees - theta.
    I did show my attempt at it, i couldn't get further.
  5. Apr 18, 2007 #4


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    Certainly, since the angles in a triangle add to [itex]2\pi[/itex] radians, [itex]B= 2\pi- \lambda- (\pi/2- \theta)= 3\pi/2- (\theta- \lambda)[/itex].
    Okay, using sin(a+ b)= sin(a)cos(b)- cos(a)sin(b)[/itex], what is
    [itex] sin(3\pi/2+ (-(\theta- \lambda)))[/itex]?
  6. Apr 18, 2007 #5


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    The angles of a triangle add upto [itex]\pi[/itex] radians
    thus [itex]B=\pi-\lambda-(\pi/2-\theta)=\pi/2+(\theta-\lambda)[/itex]
    The expression you require is therefore [itex]\sin(\pi/2+(\theta-\lambda))[/itex] = ?
  7. Apr 18, 2007 #6

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