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MathNet 2017-part-01 — 176 problems (EN–VI) Question 102

Math Olympiad Vault · MathNet 2017-part-01 — 176 problems (EN–VI)

Question 102

Consider a triangle $ABC$ and squares $ABDE$ and $ACFG$ constructed externally on its sides. The segments $BG$ and $EC$ intersect at $P$.
Question illustration
a) Prove that triangles $BAG$ and $EAC$ are congruent.
b) Since these two triangles are congruent and have the point $A$ in common, we can rotate one of them about the point $A$ to obtain the other. Determine the angle of rotation and compute the angle $\angle BPC$.