Question

Please help explain what I did wrong
Express the complex number in trigonometric form. -2i

Answer 1

I got 2(cos 90° + i sin 90°)
but that was wrong and I don't understand why.

Answer 2

@satellite73

Answer 3

ok cos(90 deg)=0
and sin(90 deg)=1
so you have
2(0+i*1)
2(i*1)
2(i)
2i

Answer 4

but you wanted -2i

Answer 5

why don't you just change 2 to -2

Answer 6

or you could go with changing the angle from 90 deg to 270 deg
since sin will be negative 1there

Answer 7

let me know if you need more assistance @hermom1967

Answer 8

So it would be 2(cos 270° + i sin 270°)?

Answer 9

Is that because it's in a different quadrant?

Answer 10

right since cos(270 deg)=0 and sin(270 deg)=-1
so you would have 2(0+i[-1])
=2[i[-1]]
=2[-i]
=-2i

Answer 11

also have you ever graphed things in the form a+bi?

Answer 12

No

Answer 13

we have a is 0 which means we don't go left or right any
but b is -2 which means we have to go down 2 units

Answer 14

Okay, I understand that

Answer 15

you can think of a+bi
as if you are plotting points (a,b)

Answer 16

you know when graphing