屁股向左:
$$ r=a(1-cos\theta)(a>0) $$
屁股向右
$$ r=a(1+cos\theta)(a>0) $$
$$ r=asin3\theta(a>0) $$
$$ r=a\theta(a>0,\theta\geqslant0) $$
$$ r^2=a^2cos2\theta $$
$$ r^2=a^2sin2\theta $$