Question

Which set is closed under subtractionWhich answer choice shows that the set of irrational numbers is not closed under addition

Answer 1

Answer:

(a) Set of rational numbers

(b) $\pi + (-\pi) = 0$

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

$a -b = c$

Where

a, b, c are of the same set.

The above is only true for rational numbers.

e.g.

$1 - 2 = -1$

$5 - 5 = 0$

$\frac{1}{2} - \frac{1}{4} = \frac{1}{2}$

$4 - 2 = 2$

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

$a -b = c$

Where

a, b, c are of the same set.

In the given options (a) to (d), only

$\pi + (-\pi) = 0$ is not close under addition because:

$\pi$ is irrational while $0$ is rational

In other words, they belong to different set