x/y=2,求x²-3xy+y²/2x²-3xy+5y²

x/y=2,求x²-3xy+y²/2x²-3xy+5y²
x/y=2,求x²-3xy+y²/2x²-3xy+5y²

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

(x²-3xy+y²)/(2x²-3xy+5y²)　　（上下同除以y^2)
=[(x/y)²-3(x/y)+1]/[2(x/y)²-3(x/y)+5]
=(4-6+1)/(8-6+5)
=-1/7

x/y=2
x=2y
x²-3xy+y²/2x²-3xy+5y²
=4y²-3*2y*y+y²/2*4y²-3*2y*y+5y²
=-y²/7y²
=-1/7

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