How do I write the trig form of -2i?

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- May 14th 2009, 05:30 PMjumpman23Trig Form
How do I write the trig form of -2i?

- May 14th 2009, 05:36 PMmr fantastic
- May 14th 2009, 05:39 PMjumpman23
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) - May 14th 2009, 07:33 PMyeongil
mr fantastic means the same thing. $\displaystyle r cis \theta$ is a shorthand way of writing $\displaystyle r(cos \theta + i sin \theta)$, so

$\displaystyle -2i = 2cis \left( -\frac{\pi}{2} \right) = 2\left[cos \left( -\frac{\pi}{2} \right) + i sin \left( -\frac{\pi}{2} \right)\right]$.

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