let $abc$ be a triangle. let $a 1$ and $c 2$ be points on $ab$ and $cb$, respectively, such that $a 1 c 2$ is parallel to $ac$. let $b 1$ and $a 2$ be points on $bc$ and $ac$, respectively, such that $b 1 a 2$ is parallel to $ba$. let $c 1$ and $b 2$ be points on $ca$ and $ba$, respectively, such that $c 1 b 2$ is parallel to $cb$. given that$[abc]