x-y/2x+2y与xy/(x+y)^22x+2y与(x+y)^2的最小公倍数是2(x+y)^2x-y/2x+2y=x-y/2(x+y)=(x-y)(x+y)/2(x+y)^2=x^2-y^2/2(x+y)^2xy/(x+y)^2=2xy/2(x+y)^22.2mn/4m^2-9与2m-3/2m+34m^2-9=(2m)^2-3^2=（2m+3）(2m-3)与2m+3的...