Question

How do you multiply `(2sqrt5)^2`?

Answer 1

You may use the following:
1] `(x^a)^b=x^(a*b)`
2] `rootn(x^m)=x^(m/n)`
In your case:
`(2sqrt(5))^2=2^2*5^(1/2*2)=4*5=20`