Write the complex number in the form a + bi.

3(cos 270° + i sin 270°)

Question

Write the complex number in the form a + bi.

3(cos 270° + i sin 270°)

zehanz · Answer

First try to see what the "modulus" or "absolute value" of this number is. (don't know the right term in English, but it's the distance from 0)
The argument is ... well 270° obviously, so draw the number in the complex plane.
Now you can just read off a and b.

anonymous · Answer

what do you mean draw it in a complex plane? 
here are the choices

 -3i

 3i

 3

 -3

zehanz · Answer

I thought you'd be familiar with the concept of the Complex Plane, which is just some kind of grid to put complex numbers on: a+bi means a in the horizontal direction, b in the vertical direction. See image:

zehanz · Answer

Of course, if you know what cos 270° and sin270° are, then you don't need a drawing,  just multiply them with 3 to get your answer...

anonymous · Answer

multiply 3 by cos270 and sin270 and then add them?

zehanz · Answer

No, you need to give the complex number in the form a+bi, so you need to know what a is and what b is. You cannot add them because a and bi are unlike terms, so just leave it at a+bi.

Expandig your number gives:

3cos270° +3sin270° i, so a=3cos270° and b=3sin270°

anonymous · Answer

so is the answer -3i?