quadratic

Find all positive integer values of c such that the equation x^2 - 5x + c only has roots that are real and rational. Express them in decreasing order, separated by commas.

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$x^2 - 5x + c =0$

         p        q

$x=-\frac{p}{2}\pm \sqrt{(\frac{p}{2})^2-q}$

$x=2.5\pm \sqrt{6.25-c}$

$c\in \mathbb{N_0}\ |0\le c\le6$