ax/2_1=3x+bax_2=6x+2bax_6x=2b+1（a_6）x=2b+1,x有无穷解，则a_6和2b+1均等于0,a=6,b=_1/2,a_1/b=6_1/（_1/2）=6+1/（1/2）=6+2=8
