Solution 4.3:1a

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If we draw the angle
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If we draw the angle <math>\pi/5</math> on the unit circle, then it will have an ''x''-coordinate that is equal to <math>\cos \pi/5\,</math>.
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<math>{\pi }/{5}\;</math>
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on a unit circle, then it will have an
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<math>x</math>
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-coordinate that is equal to
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<math>{\cos \pi }/{5}\;</math>
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.
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FIGURE 1 FIGURE 2
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[[Image:4_3_1_a.gif||center]]
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the line
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<math>x={\cos \pi }/{5}\;</math
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the line
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<math>x={\cos \pi }/{5}\;</math>
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In the figures, we see also that the only other angle between <math>0</math> and <math>2\pi</math> which has the same cosine value, i.e. same ''x''-coordinate, is the angle <math>v=-\pi/5+2\pi = 9\pi/5</math> on the opposite side of the ''x''-axis.
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In the figures, we see also that the only other angle between
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<math>0</math>
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and
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<math>2\pi </math>
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which has the same cosine value, i.e. same
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<math>x</math>
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-coordinate, is the angle
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<math>v=-\frac{\pi }{5}+2\pi =\frac{9\pi }{5}</math>
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on the opposite side of the
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<math>x</math>
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-axis.
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Current revision

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

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

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