Question 513981
I think that you are being asked to simplify the expression:

{{{ 2*sqrt(45) - 2*sqrt(5) }}}

The important thing to remember here is that you can break up the square root of a product into a product of square roots:

{{{ sqrt(ab) = sqrt(a)*sqrt(b) }}}

(Note: it is NOT true that {{{sqrt(a + b) = sqrt(a) + sqrt(b)}}} --- for example, {{{sqrt(9 + 16)}}} does not equal {{{sqrt(9) + sqrt(16)}}})

We want to break up 45 into a product of a number times a perfect square.  One way to do this is:

{{{45 = 9 * 5}}}

So {{{sqrt(45) = sqrt(9 * 5) = sqrt(9)*sqrt(5) = 3*sqrt(5) }}}

Thus we can rewrite our original expression as:

{{{ 2*sqrt(45) - 2*sqrt(5) = 2 * (3 * sqrt(5)) - 2*sqrt(5) = 6*sqrt(5) - 2*sqrt(5) = 4*sqrt(5) }}}