1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?这是道数学题.
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![1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?这是道数学题.](/uploads/image/z/74240-8-0.jpg?t=1%2F2%2B1%2F6%2B1%2F12%2B1%2F20%2B1%2F30%2B1%2F42%2B1%2F56%2B1%2F72%2B1%2F90%3D%3F%E8%BF%99%E6%98%AF%E9%81%93%E6%95%B0%E5%AD%A6%E9%A2%98.)
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?这是道数学题.
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?这是道数学题.
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/72+1/90=?这是道数学题.
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
等于9/10
希望能帮到你。
对
原式=1-1/2+1/2-1/3+1/3-1/4……+1/9-1/10
=1-1/10
=9/10
=1/(1*2)+1/(2*3)+········1/(9*10)
=(1-1/2)+(1/2-1/3)+········(1/9-1/10)
括号去掉
=1-1/10
=9/10
=1/2+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)+(1/7-1/8)+(1/8-1/9)+(1/9-1/10)=1-1/10 =9/10
1/(1*2)+1/(2*3) +1/(3*4)+1/(4*5)+1/(5*6)+1/(6*7)+1/(7*8)+1/(8*9)+1/(9*10)
=1-1/2+1/2-1/3+1/3-1/4+....+1/8-1/9+1/9-1/10
=1-1/10
=9/10
=1-1/2+1/2-1/3+...-1/10=0.9
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+。。。。+1/9-1/10
=1-1/10
=9/10