1.原式=1-2+3-4+5-6+7-8+9+1/2-5/6+1/12-19/20+1/30-41/42+1/56-71/72+1/90
=5+1/2-5/6+1/12-19/20+1/30-41/42+1/56-71/72+1/90
=1+1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
=1+1-1/2+1/2-1/3+1/3-1/4+……+1/9-1/10
=2-1/10
=1又9/10
2.原式=(104/99+104/33+104/11)÷(100/99+100/33+100/11)
=[104*(1/99+1/33+1/11)]÷[100*(1/99+1/33+1/11)]
=104÷100
=26/25
打字不易,