Question 24
Rectangles $BCC_1B_2$, $CAA_1C_2$, and $ABB_1A_2$ are erected outside an acute triangle $ABC$. Suppose that
$$
\angle BC_1C + \angle CA_1A + \angle AB_1B = 180^\circ.
$$
Prove that lines $B_1C_2$, $C_1A_2$, and $A_1B_2$ are concurrent.
$$
\angle BC_1C + \angle CA_1A + \angle AB_1B = 180^\circ.
$$
Prove that lines $B_1C_2$, $C_1A_2$, and $A_1B_2$ are concurrent.