2.若m等于它的倒数,则分式m-2/m^2-4÷m^2-3m/m-3的值为 A.-1 B.3 C.-1或3 D.-4/18.已知x-3y=0,求x^2-2xy+y^2/2x+y乘（x-y)的值.4.已知a/1+b/1=2/1,则a+b/ab的值是 A.2/1 B.-2/1 C.2 D.-25.式子x+2/x+1÷2x+3/x-2有意义,则x应满足

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