(2x-3y)/4+2/5(x+2y)=13/4(2x-3y)-(x+2y)/5=-4令 2x-3y =m x+2y = n 则:m/4 +2n/5 = 1 ……①3m/4 -n/5 = -4 ……②①+②×2 得7m/4 = -7m= -4n = 5得新方程组:2x- 3y =-4 ……③ x+2y = 5 ……④④×2 - ③ 得7y = 14y = 2x = 1