Question

Let $\mathbf{r}_{0}=\left(x_{0}, y_{0}\right)$ be a fixed vector in $R^{2}$. In each part, describe in words the set of all vectors $\mathbf{r}=(x, y)$ that satisfy the stated condition. (a) $\left\|\mathbf{r}-\mathbf{r}_{0}\right\|=1$ (b) $\left\|\mathbf{r}-\mathbf{r}_{0}\right\| \leq 1$ (c) $\left\|\mathbf{r}-\mathbf{r}_{0}\right\|>1$