计算:x^2-y^2/x^2-9y^2+(x-2y)^2/9y^2-x^2+5y^2-4xy/x^2-9y^2

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计算:x^2-y^2/x^2-9y^2+(x-2y)^2/9y^2-x^2+5y^2-4xy/x^2-9y^2
计算:x^2-y^2/x^2-9y^2+(x-2y)^2/9y^2-x^2+5y^2-4xy/x^2-9y^2

计算:x^2-y^2/x^2-9y^2+(x-2y)^2/9y^2-x^2+5y^2-4xy/x^2-9y^2
原式=(x²-y²)/(x²-9y²)-(x²-4xy+4y²)/(x²-9y²)+(5y²-4xy)/(x²-9y²)
=(x²-y²-x²+4xy-4y²+5y²-4xy)/(x²-9y²)
=0/(x²-9y²)
=0