put into normal form the isometry of $u$ in $\mathbb{R}^2$

Question

Could anyone help me in this :

put into normal form the isometry of $u$ in $\mathbb{R}^2$ that maps $(0,0),(1,0),(0,1)\to (2,-1),(1,-1),(2,0)$ respectively, and the hint is given that $u=r^{\epsilon}st$ is a normal form. thanks for helping.