元鼍:谁能巧算1-1/2-1/6-1/12-1/20-1/30-1/42-1/56-1/72-1/90
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1-1/2-1/6-1/12-1/20-1/30-1/42-1/56-1/72-1/90
=1/(1*1)-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)
因为1/(x*y)=1/x-1/y
所以原式=1/1-1/2+1/2-1/3+1/3-1/4+...-1/10=1-1/10=9/10
1/6=1/2-1/3
1/12=1/3-1/4
......
1/90=1/9-1/10
所以原式=1-1/2-(1/2-1/3)……-(1/9-1/10)=1-1/10=9/10
原式=1-1/2-(1/2-1/3)……-(1/9-1/10)=1-1/10=9/10
谁能巧算1-1/2-1/6-1/12-1/20-1/30-1/42-1/56-1/72-1/90
1+1/1+2/=??
(1/2005-1)(1/2004-1)........(1/3-1)(1/2-1)
1+1/(1+2)+1/(1+2+3)+...+1/(1+2+3+...+100)
1+1/1+2+1/1+2+3+......+1/1+2+3+......+10
1/1+1/2+1/3+1/4+。。。。+1/N 是多少
(1-1/2^2)(1-1/3^2)....(1-1/10^2)
(1-1/2^2)(1-1/3^2)....(1-1/10^2)
s=1/1+1/1!+1/2!+1/3!+1/4!+....+1/25!
3/2=2+1/1*2=1/1+1/2