[" 23.The solution of the differential equation "(x+y)(dx-dy)=dx+dy" is "[20)" ."6" c "],[[" (a) "x-y=log(x+y)+C," (b) "x+y=log(x-y)+C],[" (c) "x^(2)+y^(2)=x+y+C," (d) "x^(2)-y^(2)=x+y+C," Ans."]]