Točkama
![A](/media/m/5/a/e/5ae81275ee67d638485e903bdc0e9cde.png)
,
![B](/media/m/c/e/e/ceebc05be717fa6aab8e71b02fe3e4e3.png)
i
![C](/media/m/5/a/b/5ab88f3f735b691e133767fe7ea0483c.png)
parabole povučene su tangente na tu parabolu. One se u parovima sijeku u točkama
![K](/media/m/e/1/e/e1ed1943d69f4d6a840e99c7bd199930.png)
,
![L](/media/m/f/c/1/fc1ae4eb78da7d1352cbf1f8217ab286.png)
i
![M](/media/m/f/7/f/f7f312cf6ba459a332de8db3b8f906c4.png)
tako da je
![KL](/media/m/b/1/a/b1ab64b407588444cd365224f9b482b4.png)
tangenta u točki
![A](/media/m/5/a/e/5ae81275ee67d638485e903bdc0e9cde.png)
,
![KM](/media/m/0/1/c/01ca9badbb81b31fdf7b3e19f0f0c6c6.png)
tangenta u točki
![B](/media/m/c/e/e/ceebc05be717fa6aab8e71b02fe3e4e3.png)
, a
![LM](/media/m/c/4/a/c4aa56ea011437258c94dd4925ad7c32.png)
tangenta u točki
![C](/media/m/5/a/b/5ab88f3f735b691e133767fe7ea0483c.png)
. Presjek pravca
![AC](/media/m/6/4/7/647ef3a5d68f07d59d84afe03a9dc655.png)
i paralele s osi parabole kroz točku
![B](/media/m/c/e/e/ceebc05be717fa6aab8e71b02fe3e4e3.png)
je točka
![N](/media/m/f/1/9/f19700f291b1f2255b011c11d686a4cd.png)
. Dokaži da je četverokut
![KLMN](/media/m/5/9/0/5906903433d8aca833f74f8c34b46b24.png)
paralelogram.
%V0
Točkama $A$, $B$ i $C$ parabole povučene su tangente na tu parabolu. One se u parovima sijeku u točkama $K$, $L$ i $M$ tako da je $KL$ tangenta u točki $A$, $KM$ tangenta u točki $B$, a $LM$ tangenta u točki $C$. Presjek pravca $AC$ i paralele s osi parabole kroz točku $B$ je točka $N$. Dokaži da je četverokut $KLMN$ paralelogram.