Question

Write in form a√b √20×√2

Answer 1

Sqrt20 * sqrt2 = sqrt 40 = sqrt4 * sqrt10  = 2 sqrt10

Answer 2

I would first suggest you to find the square root of 20. This means that you need to find two factors, one of which needs to be a perfect square. Seems like 4 x 5 can work because 4 is a perfect square. 

So $\sqrt{20}$ can also be written as $\sqrt{4} \times \sqrt{5}$. We know that the square root of 4 is 2. Thus, the square root of 20 is 2 times the square root of 5 ($2 \sqrt{5}$). 

We now have $2 \sqrt{5} \times \sqrt{2}$ and since 2 is not a perfect square we cannot really simplify it any further. Therefore, we just multiply the square root of 5 and the square root of 2 because they are under the radical sign. So we get $2 \sqrt{5 \times 2} = 2\sqrt{10}$.