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Uttrykk

Posted: 21/12-2009 14:12
by Wentworth
Hei! :)

Hvordan blir denne:
[tex]-cos(\frac{9 \pi}{5})-cos(\frac{\pi}{5})[/tex]

lik denne:

[tex]-2cos(\frac{\pi}{5})[/tex]

?

Posted: 21/12-2009 14:15
by Gustav
[tex]\cos(\frac{9\pi}{5})=\cos(2\pi-\frac{\pi}{5})=\cos(-\frac{\pi}{5})=\cos(\frac{\pi}{5})[/tex]

Posted: 21/12-2009 14:24
by Wentworth
Å selvfølgelig, det er jo periodisk.Eureka plutarco :P