Answer:
(a) Set of rational numbers
(b)
Step-by-step explanation:
Solving (a): Set that is closed under subtraction
The solution to this is rational numbers.
For a set of number to be closed under subtraction, the following condition must be true
Where
a, b, c are of the same set.
The above is only true for rational numbers.
e.g.
The operations and the result in the above samples are rational numbers.
Solving (b): Choice not close under addition[See attachment for options]
As stated in (a)
For a set of number to be closed under subtraction, the following condition must be true
Where
a, b, c are of the same set.
In the given options (a) to (d), only
is not close under addition because:
is irrational while
is rational
<em>In other words, they belong to different set</em>
