From Förberedande kurs i matematik 1

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Line 5:		Line 5:
	-coordinate that is equal to		-coordinate that is equal to
	<math>{\cos \pi }/{5}\;</math>		<math>{\cos \pi }/{5}\;</math>
-	.
-	FIGURE 1 FIGURE 2	+
		+	<center> [[Image:4_3_1_a.gif]] </center>
		+
	the line		the line
	<math>x={\cos \pi }/{5}\;</math		<math>x={\cos \pi }/{5}\;</math
-	the line	+
-	<math>x={\cos \pi }/{5}\;</math>	+

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Revision as of 10:11, 29 September 2008

If we draw the angle \displaystyle {\pi }/{5}\; on a unit circle, then it will have an \displaystyle x -coordinate that is equal to \displaystyle {\cos \pi }/{5}\;

the line \displaystyle x={\cos \pi }/{5}\;

In the figures, we see also that the only other angle between $0\; and$\displaystyle 2\pi which has the same cosine value, i.e. same \displaystyle x -coordinate, is the angle \displaystyle v=-\frac{\pi }{5}+2\pi =\frac{9\pi }{5} on the opposite side of the \displaystyle x -axis.