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isosceles inside a parallelogram wanted, midpoint, projection 2006 Portugal p4

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October 13, 2020
geometryparallelogramisosceles

Problem Statement

In the parallelogram [ABCD],E[ABCD], E is the midpoint of [AD][AD] and FF the orthogonal projection of BB on [CE][CE]. Prove that the triangle [ABF][ABF] is isosceles. https://1.bp.blogspot.com/-DLmFg8ayEQ4/X4XMohA5TjI/AAAAAAAAMnk/thlIKnNUiCkuu9cg1Aq7Zltz8SenmFWuwCLcBGAsYHQ/s0/2006%2Bportugal%2Bp4.png
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