IMO 2015 zadatak 4
Kvaliteta:
Avg: 3,0Težina:
Avg: 6,0 Neka je
opisana kružnica trokuta
i
njeno središte. Kružnica
sa središtem
siječe dužinu
u točkama
i
, tako da su točke
,
,
i
u parovima različite i leže na pravcu
tim redom. Neka su
i
sjecišta kružnica
i
takva da točke
,
,
,
i
leže na kružnici
tim redom. Neka je
drugo sjecište opisane kružnice trokuta
i dužine
. Neka je
drugo sjecište opisane kružnice trokuta
i dužine
.
Pretpostavlja se da su pravci
i
različiti i da se sijeku u točki
. Dokaži da točka
leži na pravcu
.
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Pretpostavlja se da su pravci
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Izvor: Međunarodna matematička olimpijada 2015, drugi dan