Question

Express the complex number in trigonometric form.

-4
1) (cos 270° + i sin 270°)
2) 4(cos 90° + i sin 90°)
3) 4(cos 0° + i sin 0°)
4) 4(cos 180° + i sin 180°)

Answer 1

What's the imaginary part of "-4"?

Answer 2

okay, i want to show you how to do this.

when you see a problem like that, always think that the complex numbers have a radius and angle. The angle shows the "signs" and whether or not the number is going to be purely imaginary or real.

the amplitude in this case is 4. What we need to do is define the angle. (in order to exclude the imaginary parts and get -real ones)

so we have 4(cos(x)+isin(x))

what should x be, in order for the sine to be 0 and the cosine -1?
x=pi or 180 degrees.

Answer 3

imaginary part is 0

Answer 4

please read my comment

Answer 5

didnt understand

Answer 6

ok, the answer is 4), but it will do you good to try to understand it

Answer 7

ok, thanks i'll do my best