为了我方便写,假设x-y为n,x+y为m,所以n/m=2,m/n=1/2
代数式为n/(3*m)-m/(2*n)=n/(3m)-m/(2n)=1/3X(n/m)-1/2X(m/n)=2X1/3-1/2X1/2=2/3-1/4=5/12