U tetivnom četverokutu
![ABCD](/media/m/9/c/e/9ce25711ba18d9663b73c3580de4bf5a.png)
je
![\overline{AC}](/media/m/d/9/5/d95354f0f833a5fda9c16a01a878c14f.png)
promjer, a
![O](/media/m/9/6/0/9601b72f603fa5d15addab9937462949.png)
središte opisane kružnice. Neka je
![S](/media/m/c/6/3/c63593c3ec0773fa38c2659e08119a75.png)
presjek pravaca
![AD](/media/m/6/9/6/69672822808d046d0e94ab2fa7f2dc80.png)
i
![BC](/media/m/5/0/0/5005d4d5eac1b420fbabb76c83fc63ad.png)
, a
![T](/media/m/0/1/6/016d42c58f7f5f06bdf8af6b85141914.png)
presjek
![AB](/media/m/5/2/9/5298bd9e7bc202ac21c423e51da3758e.png)
i
![CD](/media/m/8/9/5/895081147290365ccae028796608097d.png)
. Dokaži da opisana kružnica trokutu
![\triangle OBD](/media/m/5/d/1/5d1e152e790938763a006ac27190d8e9.png)
siječe dužine
![\overline{AS}](/media/m/5/3/5/53591524c44de3a867cda93524655ef8.png)
i
![\overline{AT}](/media/m/7/d/9/7d97b6f3597a7182bb46e658b6cb82c2.png)
u polovištima.
%V0
U tetivnom četverokutu $ABCD$ je $\overline{AC}$ promjer, a $O$ središte opisane kružnice. Neka je $S$ presjek pravaca $AD$ i $BC$, a $T$ presjek $AB$ i $CD$. Dokaži da opisana kružnica trokutu $\triangle OBD$ siječe dužine $\overline{AS}$ i $\overline{AT}$ u polovištima.