What is 9 square root of 40 simplified?

##9sqrt(40)## = ##9sqrt(4*10)## = ##9*2sqrt(10)##=##18sqrt(10)##

This is because ##sqrt(A) \times sqrt(B) = sqrt(A\timesB)##

so by splitting up 40 into its factors, of 4 and 10 and 4 is a perfect square then ##sqrt(40) = sqrt(4) \times sqrt(10)## = ##2sqrt(10)##

It follows then that ##9sqrt(40) = 9 \times 2sqrt(10)##

which is ##18sqrt(10)##