How do you simplify Square root of 63 - Square root of 28?

##sqrt (7)##

##sqrt (63)## - ##sqrt (28)##

the factors of 63 are 7 and 9. 9 is a perfect square so therefore ##sqrt (63)## is ##3sqrt (7)##

the factors of 28 are 7 and 4. 4 is a perfect square so therefore ##sqrt (28)## is ##2sqrt (7)##

then, simplify:

##3sqrt (7)## - ##2sqrt (7)## = ##3-2sqrt (7)## = ##1sqrt (7)## or ##sqrt (7)##