谁能帮我做一道题 -1/6-1/12-1/20-1/30…-1/420急用!
来源:学生作业帮助网 编辑:作业帮 时间:2024/07/18 08:21:09
![谁能帮我做一道题 -1/6-1/12-1/20-1/30…-1/420急用!](/uploads/image/z/100345-49-5.jpg?t=%E8%B0%81%E8%83%BD%E5%B8%AE%E6%88%91%E5%81%9A%E4%B8%80%E9%81%93%E9%A2%98+%EF%BC%8D1%EF%BC%8F6%EF%BC%8D1%EF%BC%8F12%EF%BC%8D1%EF%BC%8F20%EF%BC%8D1%EF%BC%8F30%E2%80%A6%EF%BC%8D1%EF%BC%8F420%E6%80%A5%E7%94%A8%21)
谁能帮我做一道题 -1/6-1/12-1/20-1/30…-1/420急用!
谁能帮我做一道题 -1/6-1/12-1/20-1/30…-1/420
急用!
谁能帮我做一道题 -1/6-1/12-1/20-1/30…-1/420急用!
1/6+1/12+1/20+1/30+...+1/420
=1/2×3+1/3×4+1/4×5+1/5×6+...+1/20×21
=(1/2-1/3)+(1/3-1/4)+(1/4-1/5)+(1/5-1/6)+...+(1/20-1/21)
=1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+...+1/20-1/21
=1/2-1/21
=19/42
所以-1/6-1/12-1/20-1/30-……-1/420=-19/42
-1/6-1/12-1/20-1/30…-1/420
=-(1/2*3+1/3*4+1/4*5+....+1/20*21)
=-(1/2-1/3+1/3-1/4+.....+1/20-1/21)
=-(1/2-1/21)
=-19/42
-1/6-1/12-1/20-1/30…-1/420
=-(1/2*3+1/3*4+1/4*5+....+1/20*21)
=-(1/2-1/3+1/3-1/4+.....+1/20-1/21)
=-(1/2-1/21)
=-19/42
这是一个原理
-1/6-1/12-1/20-1/30…-1/420
=-(1/2*3+1/3*4+1/4*5+....+1/20*21)
=-(1/2-1/3+1/3-1/4+.....+1/20-1/21)
=-(1/2-1/21)
=-19/42
如果那不是负号就是这样:
1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+......-1/20+1/21
=1/2-1/20
=10/20-1/20
=19/20