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(117) 5

Part of 1986 Tournament Of Towns

Problems(1)

TOT 117 1986 Spring S5 circumcenter lies on other circumcircle, inside #

Source:

8/29/2019
The bisector of angle BADBAD in the parallelogram ABCDABCD intersects the lines BCBC and CDCD at the points KK and LL respectively. It is known that ABCDABCD is not a rhombus. Prove that the centre of the circle passing through the points C,KC, K and LL lies on the circle passing through the points B,CB, C and DD.
geometrycircumcirclecircucenterparallelogram