A square and some other points

Let \(ABCD\) be a square and \(P\) be a point on the side \(CD\) (\(P\neq C\) and \(P\neq D\) ). Let \(AQ\) and \(BR\) be heights in the triangle \(ABP\), and let \(S\) be the interesection point of lines \(CQ\) and \(DR\). Prove that \(\angle ASB=90°\).

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A square and some other points

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