作业帮（1）x-y/x-2y÷x^2-y^2/x^2-4xy+4y^2(2)3a/a+b - 3b/a+b(3)x+3/x^2-9 + 3/x-3(4)x^2/x+y - x+y(5)(a^2/a-3 + 9/3-a)÷a+3/a
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（1）x-y/x-2y÷x^2-y^2/x^2-4xy+4y^2(2)3a/a+b - 3b/a+b(3)x+3/x^2-9 + 3/x-3(4)x^2/x+y - x+y(5)(a^2/a-3 + 9/3-a)÷a+3/a
（1）x-y/x-2y÷x^2-y^2/x^2-4xy+4y^2
(2)3a/a+b - 3b/a+b
(3)x+3/x^2-9 + 3/x-3
(4)x^2/x+y - x+y
(5)(a^2/a-3 + 9/3-a)÷a+3/a
（1）x-y/x-2y÷x^2-y^2/x^2-4xy+4y^2(2)3a/a+b - 3b/a+b(3)x+3/x^2-9 + 3/x-3(4)x^2/x+y - x+y(5)(a^2/a-3 + 9/3-a)÷a+3/a
（1）x-y/x-2y÷x^2-y^2/x^2-4xy+4y^2=(x-y)/(x-2y)÷(x+y)(x-y)/(x-2y)²
=(x-y)/(x-2y)*(x-2y)²/(x+y)(x-y)
=(x-2y)/(x+y)
(2)3a/a+b - 3b/a+b=3a/(a+b)+3b/(a+b)
=3(a+b)/(a+b)
=3
(3)x+3/x^2-9 + 3/x-3=(x+3)/[(x+3)(x-3)]+3/(x-3)
=1/(x-3)+3/(x-3)
=4/(x-3)
(4)x^2/x+y - x+y=x²/(x+y)-(x-y)
=(x²-x²+y²)/(x+y)
=y²/(x+y)
(5)(a^2/a-3 + 9/3-a)÷a+3/a
=[a²/(a-3)+9/(3-a)]÷(a+3)/a
=[a²/(a-3)-9/(a-3)]*a/(a+3)
=[(a²-9)/(a-3)]*a/(a+3)
=[(a+3)(a-3)/(a-3)]*a/(a+3)
=(a+3)*a/(a+3)
=a
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