Lösung 4.3:2b
Aus Online Mathematik Brückenkurs 1
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Version vom 15:02, 22. Okt. 2008
If we write the angle \displaystyle \frac{7\pi }{5} as
| \displaystyle \frac{7\pi}{5} = \frac{5\pi+2\pi}{5} = \pi + \frac{2\pi }{5} |
we see that \displaystyle 7\pi/5 is an angle in the third quadrant.
The angle between \displaystyle 0 and \displaystyle \pi which has the same x-coordinate as the angle \displaystyle 7\pi/5, and hence the same cosine value, is the reflection of the angle \displaystyle 7\pi/5 in the x-axis, i.e.
| \displaystyle v = \pi -\frac{2\pi}{5} = \frac{3\pi}{5}\,\textrm{.} |
