x/y=2,求x²-3xy+y²/2x²-3xy+5y²

问题描述:

x/y=2,求x²-3xy+y²/2x²-3xy+5y²

x/y=2
x=2y
x²-3xy+y²/2x²-3xy+5y²
=(4y²-6y²+y²)/(8y²-6y²+5y²)
=-y²/7y²
=-1/7