Why is

r(cos(-x) + isin(-x) = r(cos(x) - isin(x))?

Where does the negative in the cos go?

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- Apr 16th 2007, 10:01 AMmathshelpneededcomplex numbers, a question
Why is

r(cos(-x) + isin(-x) = r(cos(x) - isin(x))?

Where does the negative in the cos go? - Apr 16th 2007, 10:05 AMPlato
The cosine function is an even function: cos(-x)=cos(x).

The sine function is an odd function: sin(-x)=-sin(x).