x/y=4/3,求xy-3y²/x²-9y²的值

x/y=4/3,求xy-3y²/x²-9y²的值

因为x/y=4/3
所以(xy-3y²)/(x²-9y²)
=y(x-3y)/(x+3y)(x-3y)
=y/(x+3y)
=1/(x/y+3)
=1/(4/3+3)
=3/13
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