由题意的：
x/3y=(6x-15y)/x
x²=18xy-45y²
x²-18xy+45y²=0
(x-3y)(x-15y)=0
x=3y或x=15y
x/3y=y/(2x-5y)
3y²=2x²-5xy
2x²-5xy-3y²=0
(x-3y)(2x+y)=0
x=3y或x=-y/2
综上所述：x=3y
则(4x²-5xy+6y²)/(x²-2xy+3y²)=9/2
x/3y=(6x-15y)/x
x²=18xy-45y²
x²-18xy+45y²=0
(x-3y)(x-15y)=0
x=3y或x=15y
x/3y=y/(2x-5y)
3y²=2x²-5xy
2x²-5xy-3y²=0
(x-3y)(2x+y)=0
x=3y或x=-y/2
所以
x=3y
(4x²-5xy+6y²)/(x²-2xy+3y²)
=[4*(3y)²-5*3y*y+6y²)]/[(3y)²-2*3y*y+3y²]
=(36y²-15y²+6y²)/(9y²-6y²+3y²)
=27y²/6y²
=27/6
=4.5
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