Question

Express the complex number in trigonometric form.

-2i

2(cos 180° + i sin 180°)

2(cos 90° + i sin 90°)

2(cos 270° + i sin 270°)

2(cos 0° + i sin 0°)

Answer 1

since you have choices it should be an easy check
see which one works

Answer 2

\[ 2(cos 180° + i \sin 180°)=2(-1+0)=-2\] so not that one

Answer 3

but what if i didn't have those choices?what would i do then?

Answer 4

then you would have a bit of work to do but not in this example because this is an easy one

Answer 5

to write
\[2i\] as
\[r(\cos(\theta)+i\sin(\theta))\] you need two numbers, \(r\) and \(\theta\)

Answer 6

I can't believe how often this question shows up lol.
It's like every couple of hours I see a new person posting this exact question.

Answer 7

2 tells you its r= 2
-i tells you its \(\theta\) = -90

Answer 8

\(r\) is easy it is \(r=|-2i|\) which is pretty clearly \(2\)

Answer 9

@zepdrix ikr

Answer 10

pretty sure the same questions show up around the same day because a lot of the home school kids are in the same section/s and having the same issues with the more difficult problems

Answer 11

you also need \(\theta\) which is easy in this case as well

Answer 12

home school
an oxymoron if ever there was one
more like "homescam"
which i had gotten in on it though...

Answer 13

lol yeah, I think it would have been bad if I had gotten in on it though, probably wouldn't be where I am today if I didn't actually >>learn<< things

Answer 14

haha.thnku sooooooo much guys!