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Math Help - HELPP Write complex number in polar form.

  1. #1
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    HELPP Write complex number in polar form.

    How would I write -4i in polar form? I know that i solve for y..and I get for but I'm not sure where to go from there.
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  2. #2
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    For any complex number a + bi, it can be expressed in the form \mbox{r cis} \,\,\theta.

    r = \sqrt{a^2 + b^2}

    \theta = \arctan{\left(\frac{b}{a}\right)}

    For your question however you should be able to see the number lies on the im axis and so the angle is \frac{-\pi}{2} and there is no real part so r = 4
    Last edited by nzmathman; December 14th 2008 at 12:44 PM.
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     - 4i = 4\left( {\cos \left( {\frac{{ - \pi }}{2}} \right) + i\sin \left( {\frac{{ - \pi }}{2}} \right)} \right) = 4e^{i\frac{{ - \pi }}{2}}
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