Hello there.
First, assume the numbers
such that they satisties both affirmations:
- The sum of the squares of two numbers is
. - The product of the two numbers is
.
With these informations, we can set the following equations:

Multiply both sides of the second equation by a factor of
:

Make 

We can rewrite the expression on the left hand side using the binomial expansion in reverse:
, such that:

The square of a number is equal to
if and only if such number is equal to
, thus:

Substituting that information from
in
, we get:

Calculate the square root on both sides of the equation:

Once again with the information in
, we have that:

The set of solutions of that satisfies both affirmations is:

This is the set we were looking for.
3, 6, and 12.
18 times 2 is 36 so 1 1/2 times 2 is 3
18 times 4 is 72 so 1 1/2 times 4 is 6
18 times 8 is 144 so 1 1/2 times 8 is 12
All you have to do is use the Triangle Inequality Theorem, which states that the sum of two side lengths of a triangle is always greater than the third side. If this is true for all three combinations of added side lengths, then you will have a triangle.
okay it appears to be 3,3 missing
its goes 3,3,3,9,4,4,4,9,5,5,5,9