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Math Help - Trig Form

  1. #1
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    Exclamation Trig Form

    How do I write the trig form of -2i?
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  2. #2
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    Quote Originally Posted by jumpman23 View Post
    How do I write the trig form of -2i?
    You mean the polar form. Have you got class notes or a textbook that give examples?

    -2i = 2 \text{cis} \left( - \frac{\pi}{2}\right).
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  3. #3
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    No we have not learned about the polar form..

    The textbook says to write the trigonometric form of (-2i).

    and that it should look something like this: z = r(cosX + isinX)
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  4. #4
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    mr fantastic means the same thing. r cis \theta is a shorthand way of writing  r(cos \theta + i sin \theta), so
    -2i = 2cis \left( -\frac{\pi}{2} \right) = 2\left[cos \left( -\frac{\pi}{2} \right) + i sin \left( -\frac{\pi}{2} \right)\right].


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