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# [solved] Trigonometric Function watch

1. Ok, i have a test tomorrow and i've been given a proof which involves the line:

cos(-x) + isin(-x) = cos(x) - isin(x) (x = theta)

Why is this? i dont understand how that works.
2. because:

(try in your head reflecting the graphs of each in the y-axis to see WHY this is...)
3. (Original post by rhamill95)
Ok, i have a test tomorrow and i've been given a proof which involves the line:

cos(-x) + isin(-x) = cos(x) - isin(x) (x = theta)

Why is this? i dont understand how that works.
Bit rusty but think its to do with trig identities and sin(-x) = -sin(x) http://www.sosmath.com/trig/Trig5/trig5/trig5.html
4. (Original post by Hasufel)
because:

(try in your head reflecting the graphs of each in the y-axis to see WHY this is...)
(Original post by laalNick)
Bit rusty but think its to do with trig identities and sin(-x) = -sin(x) http://www.sosmath.com/trig/Trig5/trig5/trig5.html
Ok, thanks. So its to do with odd and even functions? =) il look those up now, as i havent done them in a while.. Thanks for help!

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Updated: January 22, 2014
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