第一题:2/3+2/3*5+2/5*7+2/7*9+2/9*11+2/11*13=?
来源:学生作业帮 编辑:搜搜做题作业网作业帮 分类:数学作业 时间:2024/06/24 11:43:17
第一题:2/3+2/3*5+2/5*7+2/7*9+2/9*11+2/11*13=?
第二题:1/2*5+1/5*8+1/8*11+1/11*14+1/14*17=?
第二题:1/2*5+1/5*8+1/8*11+1/11*14+1/14*17=?
![第一题:2/3+2/3*5+2/5*7+2/7*9+2/9*11+2/11*13=?](/uploads/image/z/19150879-31-9.jpg?t=%E7%AC%AC%E4%B8%80%E9%A2%98%EF%BC%9A2%2F3%2B2%2F3%2A5%2B2%2F5%2A7%2B2%2F7%2A9%2B2%2F9%2A11%2B2%2F11%2A13%3D%3F)
第一题:2/3+2/3*5+2/5*7+2/7*9+2/9*11+2/11*13=?
=1-1/3+1/3-1/5+1/5-1/7+...+1/11-1/13
=1-1/13
=12/13
第二题:1/2*5+1/5*8+1/8*11+1/11*14+1/14*17=?
=1/3[1/2-1/5]+1/3[1/5-1/8]+...+1/3[1/14-1/17]
=1/3[1/2-1/5+1/5-1/8+...+1/14-1/17]
=1/3[1/2-1/17]
=5/34
=1-1/3+1/3-1/5+1/5-1/7+...+1/11-1/13
=1-1/13
=12/13
第二题:1/2*5+1/5*8+1/8*11+1/11*14+1/14*17=?
=1/3[1/2-1/5]+1/3[1/5-1/8]+...+1/3[1/14-1/17]
=1/3[1/2-1/5+1/5-1/8+...+1/14-1/17]
=1/3[1/2-1/17]
=5/34