For any integer n greater than or equal to 1 prove the inequality
τ(n) less than or equal to 2sqrt(n)
The function is tau(n) less than or equal to 2sqrt(n)
I suppose you mean the number of divisors function.
Note that for each divisor $\displaystyle d$ (of $\displaystyle n$) $\displaystyle \frac{n}{d}$ is a divisor as well.
And at least one of the following inequalities holds $\displaystyle d\leq{\sqrt{n}}$ or $\displaystyle \frac{n}{d} \leq {\sqrt{n}}$.