已知x/y=2/7,则x²-3xy+2y²/2x²-9xy+7y²的值为

已知x/y=2/7,则x²-3xy+2y²/2x²-9xy+7y²的值为
已知x/y=2/7,则x²-3xy+2y²/2x²-9xy+7y²的值为

已知x/y=2/7,则x²-3xy+2y²/2x²-9xy+7y²的值为
原式=(x-2y)(x-y)/(2x-7y)(x-y)
=(x-2y)/(2x-7y)
上下同除以y
=(x/y-2)/(2x/y-7)
=(2/7-2)/(4/7-7)
=4/15