13. As shown in the figure, $ABCD$ is a trapezoid, and the intersection point of its diagonals is $O$. Extend $AC$ to point $E$, such that $CE = AO$. Extend $DB$ to point $F$, such that $BF = DO$. If the area of $\triangle BFG$ is 2015 square centimeters, find: the area of $\triangle CGE$.
【Answer】2015

【Solution】Since $A B C D$ is a trapezoid, using the equal area transformation we have $S_{\triangle A O B}=S_{\triangle D O C}$. Using $C E=A O$, we deduce that $S_{\triangle A O B}=S_{\triangle C B E}$. Using $B F=D O$, we deduce that $S_{\triangle D O C}=S_{\triangle B C F}$. Combining $S_{\triangle A O B}=S_{\triangle D O C}$, we have $S_{\triangle C B E}=S_{\triangle B C F}$, so $S_{\triangle C B E}-S_{\triangle B C G}=S_{\triangle B C F}-S_{\triangle B C G} \Rightarrow S_{\triangle B F G}=S_{\triangle C G E}$, thus the area of $\triangle C G E$ is also 2015.