# Which of these numbers is greater: $\sqrt{5}$ or $\sqrt{4}$?

I know that this is the question of elementary mathematics but how to logically check which of these numbers is greater: $\sqrt{5}$ or $\sqrt{4}$?

It seems to me that since number $5$ is greater than $4$ and we denote $\sqrt{5}$ as $x$ and $\sqrt{4}$ as $y$ then $x^5 > y^4$.

• The LaTeX commands work if you insert a dollar sign on each side of the mathematical expression in question. I've done that for you; I hope that's OK ... – Amitesh Datta Jul 26 '13 at 9:55
• Which one is greater? $(\sqrt{5})^{n}$ or $(\sqrt{4})^{n}$? (Find a suitable $n$.) – egreg Jul 26 '13 at 9:56

## 2 Answers

$\text{}$$5^4<4^5$$\text{}$

Now, take the 20th root on both sides of the inequality if you can!

If $x_0$ is some positive natural number (or in fact any real number greater than $\tfrac{1}{\text e}$), then $$\left(\frac{\text d}{\text dx}x^x\right)_{x=x_0}=\left(x^x(\ln(x)+1)\right)_{x=x_0}>0.$$ The function is smooth and growing, so bigger numbers $x$ give bigger $x^x$.

• Yes, that's true but we're not looking at numbers of the form $x^{x}$ here; rather, we're looking at numbers of the form $x^{\frac{1}{x}}$ ... – Amitesh Datta Jul 26 '13 at 10:03
• @AmiteshDatta: Oh, yeah that's right. My bad. – Nikolaj-K Jul 26 '13 at 10:41
• No problem, Nick! I would still upvote your answer nonetheless (because it presents a new idea) but I've exhausted my daily vote limit of 40 votes. But I will upvote your answer tomorrow! – Amitesh Datta Jul 26 '13 at 11:19
• @AmiteshDatta: Don't worry, I'm not a fan of the reputation system anyway. (It makes people feel they need to write in a certain style once they got some, and on the other side, if a poster with many points posted an answer, even if it's only an OK answer, often no more answers follow. I recently spent 1500 points on bounties just to get rid of it. On the physics board, I spent about 5000 points on bounties - and I can now empirically say that it doesn't improve the answer quality. The questions which get bounties are usually so hard (or broad) that nobody bothers anyway.) – Nikolaj-K Jul 26 '13 at 11:53
• I'm sorry Nick but could you explain this to me better, or maybe draw a graph, I think I'm a little bit cofused – mike Jul 26 '13 at 12:29