Question 604351
Take advantage of the fact that {{{sqrt(xy)=sqrt(x)*sqrt(y)}}} and 45 = 9*5 to get...


{{{sqrt(45)}}}


{{{sqrt(9*5)}}}


{{{sqrt(9)*sqrt(5)}}}


{{{3*sqrt(5)}}} 



As we can see in the last step above, taking the square root of 9 gives us 3, which is why we factored 45 into 9*5. 
So {{{sqrt(45)}}} simplifies to {{{3*sqrt(5)}}}