1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?用简便算法算
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![1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?用简便算法算](/uploads/image/z/18469-37-9.jpg?t=1%2F2%2B1%2F6%2B1%2F12%2B1%2F20%2B1%2F30%2B1%2F42%2B1%2F56%2B1%2F72%2B1%2F90%3D%3F%E7%94%A8%E7%AE%80%E4%BE%BF%E7%AE%97%E6%B3%95%E7%AE%97)
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1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?用简便算法算
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?用简便算法算
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?用简便算法算
=1/1* 1/2+1/2*1/3+1/3*1/4+...+1/9*1/10
=1/1-1/2+1/2-1/3+1/3-1/4+...+1/9-1/10
=1/1-1/10
=9/10