We can use the quotient rule for this, which states that the derivative of $\frac{f}{g}$ is $\frac{f'g - fg'}{g^2}$. Here, $f = 2$ and $g = 1 - \cos\theta$. The derivative of $f$ is $0$ and the derivative of $g$ is $\sin\theta$. So, the derivative of $r(\theta)$
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