Giải thích các bước giải:
Chứng minh OHCI là hình chữ nhật
⇒ OQ = HC = HB
\(\begin{array}{l}
Do:QE//BE\\
\to \frac{{KO}}{{KB}} = \frac{{OQ}}{{BE}}\\
\to \frac{{KO}}{{KO + OB}} = \frac{{OI}}{{HB + HE}}\\
\to \frac{{KO}}{{KO + OD}} = \frac{{OQ}}{{OQ + HE}}\\
\to \frac{{KO}}{{OD}} = \frac{{OQ}}{{HE}}\left( 1 \right)\\
Do:OQ//CE\\
\to \frac{{OQ}}{{CE}} = \frac{{OI}}{{IE}}\\
\to \frac{{OQ}}{{OQ + CE}} = \frac{{OI}}{{OI + IE}}\\
\to \frac{{OQ}}{{HE}} = \frac{{OI}}{{OE}}\left( 2 \right)\\
(1)\& \left( 2 \right) \to \frac{{OK}}{{OD}} = \frac{{OI}}{{OE}}\\
\to KI//DE\\
\to KI \bot OD
\end{array}\)
