1/2+1/6+1/12+1/20+1/30+1/42=
1/2+1/6+1/12+1/20+1/30+1/42=? 答案是6/7, 解答过程是1/2+1/6+1/12+1/20+1/30+1/42=n/(n+1)=6/(6+1) 其中n=6 本人看不懂,请求解答
1/2+1/6+1/12+1/20+1/30+1/42=? 这样的题目一定是做分母的文章 看1/2=1/(1*2)=1-1/2 1/6=1/(2*3)=1/2-1/3 1/12=1/(3*4)=1/3-1/4 1/20=1/(4*5)=1/4-1/5 1/30=1/(5*6)=1/5-1/6 1/42=1/(6*7)=1/6-1/7 现在再来看1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/6-1/7 =1-1/7=6/7 答案很快就知道了. 注意1/(A*B)这样的式子.A和B相差1个数.A小与B就能化成 1/A-1/B的式子
1/2+1/6+1/12+1/20+1/30+1/42 =(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7) =1-1/7 =6/7
原式可化为: 1/(1*2)+1/(2*3)+1/(3*4)+1/(5*6)+1/(6*7) =(1/1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7)=1-1/7 =6/7 其实应该注意:1/[n*(n+1)]=1/n-1/(n+1),这样逐项相消就简化了计算。
1/2+1/6+1/12+1/20+1/30+1/42 =(1-1/2)+(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+(1/6-1/7) =1-1/7 =6/7
其实原式可化为: 1/1*2+1/2*3+1/3*4+1/5*6+1/6*7=1-1/7=6/7
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