0
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I'm guessing it gets drawn twice, but I can't see where

enter image description here

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  • $\begingroup$ Because cosine goes positive and negative. $\endgroup$ – David G. Stork Jul 21 '17 at 20:11
  • $\begingroup$ Sorry, how does that relate? $\endgroup$ – jamesson Jul 21 '17 at 20:12
  • $\begingroup$ Oh, OK, that {1,-1} at the very beginning. I don't know what that is yet, sorry. $\endgroup$ – jamesson Jul 21 '17 at 20:15
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To draw the rose only once:

PolarPlot[{{1, -1} Cos[3 t], {1, -1}}, {t, 0, Pi}]

enter image description here

Compare with

PolarPlot[{Cos[3 t], {1, -1}}, {t, 0, Pi}]

enter image description here

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  • $\begingroup$ What does that {1,-1} do, exactly? $\endgroup$ – jamesson Jul 21 '17 at 20:21
  • $\begingroup$ See updated answer $\endgroup$ – eldo Jul 21 '17 at 20:21
  • $\begingroup$ The ` {1,-1}` draws the circle around the rose $\endgroup$ – eldo Jul 21 '17 at 20:23
  • $\begingroup$ No, the one before Cos[3t], the one that returns 3 petals when you pull it :) $\endgroup$ – jamesson Jul 21 '17 at 20:24
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    $\begingroup$ What version of Mathematica? Do not get circle with V11.1. PolarPlot was upgraded in 10.0? Are you using earlier version? $\endgroup$ – m_goldberg Jul 21 '17 at 23:00

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