MathDB

4

Part of 2021 Polish Junior MO Second Round

Problems(1)

angle bisector of <BAD _|_ KL, AB+BK = AD+DL, #ABCD (2021 Polish JMO R2 p4)

Source:

4/8/2021
Points KK and LL are on the sides BCBC and CDCD, respectively of the parallelogram ABCDABCD, such that AB+BK=AD+DLAB + BK = AD + DL. Prove that the bisector of angle BADBAD is perpendicular to the line KLKL.
geometryperpendicularparallelogram