i是虚数单位，若-1+3i/1+2i=a+bi(a,b属于实数，)则a-b的值是

-1+3i/1+2i =(-1+3i)(1-2i)/(1+2i)(1-2i) =(5+i)/5 =1+1/5i =a+bi a=1 b=1/5 a-b=4/5