Sum/difference:
Let

This means that

Now, assume that
is rational. The sum/difference of two rational numbers is still rational (so 5-x is rational), and the division by 3 doesn't change this. So, you have that the square root of 8 equals a rational number, which is false. The mistake must have been supposing that
was rational, which proves that the sum/difference of the two given terms was irrational
Multiplication/division:
The logic is actually the same: if we multiply the two terms we get

if again we assume x to be rational, we have

But if x is rational, so is -x/15, and again we come to a contradiction: we have the square root of 8 on one side, which is irrational, and -x/15 on the other, which is rational. So, again, x must have been irrational. You can prove the same claim for the division in a totally similar fashion.
Answer:
I have exactly 5,621 dominoes, and, including myself, 23 people to set them all up. How many dominoes will each person set up?
You have to divide denominator by numerator to find the constant of proportionality.
Answer:
Step-by-step explanation:
Let
, a reflection over the x-axis consists in the following operation:

If we know that
and
, then the points translated over the x-axis are
and
, respectively. The most precise description of the shape is a rectangle for the following facts:
1)
and
.
2)
and
have the same x-component.
3)
and
have the same x-component.
4)
and
have the same y-component.
5)
and
have the same y-component.
A representation of the shape is included below as attachment.