Can someone help me here?

"The product of 4(cos30 + i sin30) and 3(cos90 + i sin90) is equal to..."

The answer is 6(-1 + i rad(3)) apparently but I don't know where that came from.

I can never remember how to do these for some reason...

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- Nov 4th 2009, 07:40 PMmcsquaredMultiplying CIS
Can someone help me here?

"The product of 4(cos30 + i sin30) and 3(cos90 + i sin90) is equal to..."

The answer is 6(-1 + i rad(3)) apparently but I don't know where that came from.

I can never remember how to do these for some reason... - Nov 4th 2009, 07:53 PMpickslides
Do you mean?

- Nov 4th 2009, 08:12 PMmcsquared
Yes thank you!

I'm wondering...is it possible to state that answer in cis form? - Nov 4th 2009, 11:51 PMpurebladeknight
of course - all complex numbers can be stated in cis form

just find the mod and angle in the complex graph - Nov 5th 2009, 02:08 AMHallsofIvy
That is surely the hard way! The whole

**point**of the "polar form", (also written and even ), is that

.

Here, (4 cis(30))(3 cis(90))= (12) cis(120)= 12(cos(120)+ i sin(120)). Since the numbers were given in "cis" form, I would leave the answer in that form. If you like, and so