# Math Help - proving

1. ## proving

how do you prove that there is a rational number whose square is 9?

sorry, i just started learning on proofs and have not much idea on how to think in order to solve this question..is there a certain method that i can use whenever i see proving questions?

thanks!

2. Originally Posted by alexandrabel90
how do you prove that there is a rational number whose square is 9?
$\left(\frac{3}{1}\right)^2=9$
Is that what you mean?

3. You need to find $m,n \in Z$ such that

Here's a start.

$\left(\frac{m}{n}\right)^2 = 9$

$\left(\frac{m}{n}\right)^2 = 3^2$