Polar Forms, Help!

[soccer_gal]

Hello,

I am working on a set of problems as my final exam is in a few days.
And I am having great difficulty with polar forms.

I had to expres -4i in polar form and I get 4e^ i pi/2. However, the answer keys says it should be 4e^ - pi/2 i
I don't know where the negative came from.

Also, for the next question I had to express 8e^2pi/3 i in polar form,

Comments

[phlebas]

Does it help if you draw a picture before you start with the trig functions? I suspect that would help you with both of those - if you can visualise it, the two coordinate systems make much more sense.

[soccer_gal]

Yes drawing it helped! Thanks.

[misteral]

Remember that there are usually two solutions to the equation tan θ = y/x in the interval (-π, π). For each of your questions here, you must determine which of these solutions is the correct one.

Like the poster above me has suggested, drawing a diagram would undoubtedly help you with that.

[soccer_gal]

Yes drawing the diagram helped!