1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90(写过程)
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![1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90(写过程)](/uploads/image/z/3836144-56-4.jpg?t=1%2F2%2B1%2F6%2B1%2F12%2B1%2F20%2B1%2F30%2B1%2F42%2B1%2F56%2B1%2F72%2B1%2F90%28%E5%86%99%E8%BF%87%E7%A8%8B%29)
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90(写过程)
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90(写过程)
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90(写过程)
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90
=1-1/2+1/2-1/3+1/3-1/4+......1/9-1/10
=1-1/10
=9/10