原式=2x√x+6x√y/√x+y√x/√y-x^2/√x
=(2x^2+6x√y-x^2)/√x+y√x/√y
=[(x^2+6x√y)√y+xy]/√xy
=(x^2+6xy+xy)/√xy
=(x^2y^2√x+7xy√xy)/xy