square root of 40

I'm thinking you want to simplify this.

To simplify square roots, break them down into factors like so:

$$\sqrt{40} = \sqrt{4\times10} = \sqrt{4}\sqrt{10}$$  

The square root of 4 is 2:

$$2\sqrt{10}$$

And that would be it. You wouldn't break 10 down into 2 and 5, because those numbers aren't "perfect squares." A perfect square means that you can break that number down into two of the same multiples. So, 25 and 100 would be perfect squares becasue 5x5=25 and 10x10=100.

If you have any other questions feel free to ask.