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Math Help - evaluating the following.

  1. #1
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    evaluating the following.

    evaluating
     <br /> <br />
sin(\frac{-9\pi}{4})<br /> <br />

    just wondering how they got

     <br /> <br />
\frac{-1}{\sqrt{2}}<br /> <br />

    i got

     <br /> <br />
\frac{-\sqrt{2}}{2}<br /> <br />
    but was wrong
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  2. #2
    Super Member 11rdc11's Avatar
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    Try this

    \bigg(\frac{-\sqrt{2}}{2}\bigg)\bigg(\frac{\sqrt{2}}{\sqrt{2}}\  bigg)

    \frac{-2}{2\sqrt{2}}

    \frac{-1}{\sqrt{2}}
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  3. #3
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    I got 2 root 2 as well..isn't this in the 1st quadarant...hence Sin = a positive...
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  4. #4
    Super Member 11rdc11's Avatar
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    Its in the 4th quadarant
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  5. #5
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    Quote Originally Posted by justinwager View Post
    I got 2 root 2 as well..isn't this in the 1st quadarant...hence Sin = a positive...
    yeah thats what i thought.. its wierd. dont know how they got the -1 and root 2 on the denom
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  6. #6
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    Quote Originally Posted by 11rdc11 View Post
    Its in the 4th quadarant
    yeah coz u go backyards , but it still shud be what i wrote..
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  7. #7
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    Quote Originally Posted by 11rdc11 View Post
    Try this

    \bigg(\frac{-\sqrt{2}}{2}\bigg)\bigg(\frac{\sqrt{2}}{\sqrt{2}}\  bigg)

    \frac{-2}{2\sqrt{2}}

    \frac{-1}{\sqrt{2}}
    why did u multiply it by 1 ? sqrt 2 / sqrt 2
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  8. #8
    Super Member 11rdc11's Avatar
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    To make it look like the answer provided. It doesn't change the answer since what I did to the numerator I also did to the denominator so it valid

    \frac{-\sqrt{2}}{2} = \frac{-1}{\sqrt{2}}<br />
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