I feel ridiculous asking this question because I know how simple it is, yet I can't seem to get the answer the book is getting.

Write this in a trigonometric form: -7 + 4i

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- Jun 9th 2007, 09:22 AMalreadyinuseWriting a Complex Number in Trigonometric Form
I feel ridiculous asking this question because I know how simple it is, yet I can't seem to get the answer the book is getting.

Write this in a trigonometric form: -7 + 4i - Jun 9th 2007, 09:35 AMCaptainBlack
- Jun 9th 2007, 09:45 AMalreadyinuse
I knew how to do that, but somehow I can't get the answer:

square root 65(cos2.62 + isin2.62)

**Edit:**Ack. Just saw what I did wrong.

Thanks. - Apr 13th 2009, 04:58 PMStruggle_Through
Can someone explain how this the answer becomes 2.62. I have this same problem and really don't understand how they get it. It would be the arctan of 4/7 but how do they get 2.62

Thanks. - Apr 13th 2009, 05:39 PMJhevon
it is just a matter of knowing that this is the reference angle of the one you want. you want the positive angle measured from the positive real-axis. so you need the angle which arctan(4/7) is a reference angle for, which is $\displaystyle \pi - \arctan \frac 47 \approx 2.62$

- Apr 13th 2009, 06:02 PMStruggle_Through