In Exercises 1 through 6 determine whether the indicated sets form a ring under the indicated operations.
1. S = {$a + b\sqrt{3}$ | a, b ∈ Z}, under the usual operations on real numbers
2. S = {$a + bi$ | a, b ∈ Q}, under the usual operations on complex numbers
3. S = {$\begin{bmatrix} a & b \\ 0 & a \end{bmatrix}$ | a, b ∈ R}, under matrix addition and multiplication