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If $0 < \theta <2 \pi $ then $0< \large \frac{\theta}{2} \normalsize < \pi$ and $\sin \left(\large \frac{\theta}{2}\right) >0.$ Thus, for example if $\theta = \large \frac{3 \pi}{2}$ then \[r = \sin \left(\frac{\theta}{2}\right) = \sin \left(\frac{3 \pi}{4}\right) = \frac{1}{\sqrt 2} = 0.70711\] Penny  


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