1/x -1/y =4推出y/xy - x/xy =4 ,(y-x)/xy =4,x-y = -4xy(2x+3xy-2y)/(x-4xy-y) =( 2(x-y)+3xy )/((x-y) -4xy) 因为x-y =-4xy所以原式 = (2*(-4xy)+3xy)/(-4xy-4xy) =(-8xy+3xy)/-8xy= -5xy / -8xy =5/8 ...