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# FP2: Complex numbers problem. Watch

1. Hi, I've been set a homework sheet and think I've made a mistake somewhere along this question:

Show that 1 + e^(jx) = (2cos((1/2)x))e^((1/2)jx)

My working thus far (may have mistakes in, I'm tired and braindead):

1 + e^(jx)
= 1 + cosx + jsinx
= 1 + (1/2)(2cos^2((1/2)x) + 1) + 2jsin((1/2)x)cos((1/2)x)
= (3/2) + cos^2((1/2)x) + 2jsin((1/2)x)cos((1/2)x)
= (3/2) + (2cos((1/2)x)(1/2cos((1/2)x) + jsin((1/2)x))

And naturally I would turn that last bit into e^((1/2)jx) if I had a whole cos((1/2)x), but it still wouldn't be the result I want.

Sorry if this is hard to read, but I'm hopeless with LaTeX.

Cheers.
2. On this line:

(Original post by TheDefiniteArticle)
= 1 + (1/2)(2cos^2((1/2)x) + 1) + 2jsin((1/2)x)cos((1/2)x)
The 1/2 shouldn't be there, and the +1 should be -1.

You should find that things cancel/simplify from here.
3. Well aren't I a daft ****.

Thanks.
4. (Original post by TheDefiniteArticle)
Show that .
I personally would have started with the RHS, using the following identity.

Aside: This can be shown using the fact that .

It should make life a lot easier.

I hope it helps.

Darren

Updated: March 24, 2012
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