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:
376.991 cm²
Step-by-step explanation:

Surface Area = 2π(5²) + 2π(5)(7)
= 50π + 70π
= 120π
= 376.9911184... ≈ 376.991
<h2>Derive Surface Area of A Cylinder</h2>
If you take a look at a net of a cylinder, you can see it is composed of two circles(bases) and a rectangular strip with the length of the diameter of the circle
The formula for the area of a circle = πr², and since there are 2, it is 2πr²
The formula for circumference of a circle = 2πr, and since we are multiplying that by the height by the height of the cylinder, it is 2πrh
∴ 2πr² + 2πrh
I got 3x^2 + 12x + 4. I recommend you verify my answer, so you have to combine like terms in the first expression then add all the expressions.