First, we need to show that the direct product $R \times S$ is a commutative $k$-algebra. To do this, we need to define the addition and multiplication operations on $R \times S$.
Addition: $(r_1, s_1) + (r_2, s_2) = (r_1 + r_2, s_1 + s_2)$
Multiplication: $(r_1,
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