I have included a photo below:
my questions are as follows:
- for the second one what is set ab? is it suppose to represent a U b
- What set does a/b represent? is it the equivalent to the difference of sets. "a-b"
- my question for the last one is the same as the second one, what does "ab" mean?
thanks a lot for the help, i did attempt to google it, but i do not know the key terms to google for
In all of these questions $a$ and $b$ are numbers, not sets. Therefore $ab$ simply represents the product of $a$ and $b$, and $\frac{a}{b}$ the quotient.
Note that $\in$ means "is an element of," not "is a subset of." Therefore $a \in \mathbb{Q}$ means $a$ is a rational number, not $a$ is a subset of the rational numbers.
Although it is not explicitly stated, I think you can safely assume $a$ and $b$ are real numbers. So if $a \notin \mathbb{Q}$, this means $a$ is a real number but not a rational number. (Without this assumption, it could be that $a \notin \mathbb{Q}$ because $a=\text{my cat}$, in which case the arithmetic operations don't make sense.)