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IMO 1975 — Official Contest Question 3

IMO · IMO 1975 — Official Contest

Question 3

On the sides of an arbitrary triangle $ABC$, triangles $BPC$, $CQA$, and $ARB$ are externally erected such that
$$\angle PBC=\angle CAQ=45^\circ,$$
$$\angle BCP=\angle QCA=30^\circ,$$
$$\angle ABR=\angle BAR=15^\circ.$$
Prove that $\angle QRP=90^\circ$ and $QR=RP$.