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Math 110

  1. Nov 20, 2008 #1
    1. Find the exact value of the expression arcsin(sin(5pi/9))

    2. 5pi/9 = 100 degrees and pi/9 = 20 degrees

    3. Tried pi/9 but it is wrong
  2. jcsd
  3. Nov 21, 2008 #2
    SO, 5pi/9 is 100 degree. So take sin of that. And do the arc sin of that.
    Sin(5pi/9) = .9848

    arcsin(.9848) = 80 degrees
  4. Nov 21, 2008 #3


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    Because sine is periodic, it doesn't have a true "inverse". The usual definition of Arcsine gives a value between [itex]-pi/2[/itex] and [itex]\pi/2[/itex]. [itex]5\pi/9[/itex] is not in that range. Use the facts that [itex]sin(x+ 2\pi)= sin(x)[/itex] and [itex]sin(\pi- x)= - sin(x)[/itex].
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