Show that $+: R \times R \rightarrow R$ and $\times: R \times R \rightarrow R$ are commutative binary operations,but $-: R \times R \rightarrow R$ and $\div: R_* \times R_* \rightarrow R_*$ are not commutative.

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(N/A) binary operation $\ast$ on a set $S$ is commutative if $a \ast b = b \ast a$ for all $a, b \in S$.
For addition $(+)$ on $R$: Since $a + b = b + a$ for all $a, b \in R$,the operation $+$ is commutative.
For multiplication $(\times)$ on $R$: Since $a \times b = b \times a$ for all $a, b \in R$,the operation $\times$ is commutative.
For subtraction $(-)$ on $R$: Since $a - b \neq b - a$ in general (e.g.,$3 - 4 = -1$ and $4 - 3 = 1$),the operation $-$ is not commutative.
For division $(\div)$ on $R_*$: Since $a \div b \neq b \div a$ in general (e.g.,$3 \div 4 = 0.75$ and $4 \div 3 = 1.33$),the operation $\div$ is not commutative.

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