解:5/9*2/17+4/17*2/9 =2/9*5/2*2/17+2/17*2*2/9 =(2/9+7/12)*(5/2+2) =2/9*7/12*9/2 =7/12
5/9*2/17+4/17*2/9=(10+8)/(17*9)=18/9*17=2/17
5/9*2/17+4/17*2/9=5/9*2/17+2/17*4/9=2/17*(5/9+4/9)=2/17*1=2/17