Lösung 4.3:2b
Aus Online Mathematik Brückenkurs 1
If we write the angle \displaystyle \frac{7\pi }{5} as
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.
