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Homework Help: Trig question -sin pi/4 , give the exact value?

  1. Jul 11, 2011 #1
    1. The problem statement, all variables and given/known data

    -sin pi/4 , give the exact value?
    -1/root 2 is the answer according to the book? How in the world do they get that result. What do you to make that happen?

    2. Relevant equations

    3. The attempt at a solution

    Also, is this how to do the problem? Find pi/4 on the unit circle, it's root 2 / 2, that doesn't seem to get the right answer even though that's was supposed to be the method?
  2. jcsd
  3. Jul 11, 2011 #2
    [itex]\frac{1}{\sqrt{2}}[/itex] is the same as [itex]\frac{\sqrt{2}}{2}[/itex], simply "rationalize" it by multiplying the top and bottom by [itex]\sqrt{2}[/itex]

    Basically you have the right idea, you can think of sin as the y-coordinate.
    Remember, the problem is "negative" sin pi/4.
  4. Jul 11, 2011 #3
  5. Jul 12, 2011 #4
    It is sloppy to leave a radical in the denominator.
  6. Jul 12, 2011 #5


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    Not in all cases :tongue:
    I don't think the teacher would worry so much about it when it comes to trig.
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