Complex numbers

I need help with complex numbers...

Prove:

a) cis(x)+cis(-x) = 2cos(x)

b) sin(x) = (1/2i) * (cis(x)-cis(-x))

a) cis(x) + cis(-x) = cos x + isin x + cos(-x) + isin(-x) = cos x +isin x + cos x - isin x = 2cos x

similarly,

b)cis(x) - cis(-x) = cos x + isin x - (cos(-x) + isin(-x)) = cos x + isin x - (cos x - isin x) = (2i)sin x, implying sin(x) = (1/2i) * (cis(x)-cis(-x))

OP here, thankyou so much ^_^

You're welcome. :)

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