Geometric interpretation of linear transformations

Find the matrix for the linear transformation that rotates every vector in $\mathbb{R}^{2}$ by an angle of $\pi/3$.

Let $\mathbf{u}=\left[\begin{array}{r}a\\ b\end{array}\right]$ be a unit vector in $\mathbb{R}^{2}$. Find the matrix that reflects all vectors about this vector, as shown in the following picture.