how to calculate the rank of the matrix?

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I need to calculate the rank of the $3\times 3$ matrix

$$ \begin{pmatrix} 1 & p & p^2 \\ q & 1 & q^2 \\ r^2 & r & 1 \end{pmatrix} $$

I've already tried many methods,but I can't find an easy way. Here $p$, $q$, and $r$ are all real numbers.