x+ay=5 (1) y-x=1 (2)(1)+(2)得 (a+1)y=6 则y=6/(a+1) x=y-1=6/(a+1)-1,由于方程为正整数解,则6/（a+1）是整数即a+1能被6整除得a+1=-6或-2或-3或-1或1或2或3或6解得a=-7,-4,-3,-2,0,1,2,5a为正整数,那么a的值为1,2,5...