Prove or disprove:
Proposition: $a, b, c$ are sides of a triangle if
$$ (a+b+c)\left(\frac{1}{a} + \frac{1}{b} + \frac{1}{c}\right) \lt 10$$
Note that we can easily show that (using AM $\ge$ GM for instance)
$$ (a+b+c)\left(\frac{1}{a} + \frac{1}{b} + \frac{1}{c}\right) \ge 9$$
for any positive reals $a, b, c$.
So we can restate the above statement as
Proposition: $a, b, c$ are sides of a triangle if
$$\left\lfloor (a+b+c)\left(\frac{1}{a} + \frac{1}{b} + \frac{1}{c}\right) \right\rfloor = 9$$
where $\lfloor x \rfloor$ is the integer part of $x$.
[Note: Initially I had if only if, but I have changed the statements to just be an implication]
No comments:
Post a Comment