<s>[INST] In triangle $ABC$ with circumcircle $O$, point $A_1$ is the image of $A$ under a reflection about the line $BC$. Similarly, let $B_1$ be the image of $B$ under a reflection about the line $CA$, and let $C_1$ be the image of $C$ under a reflection about the line $AB$. Prove that the triangle $A_1B_1C_1$ is similar to triangle $ABC$ with ratio $-1$.[/INST]