Giải thích các bước giải:
Theo bài ra ta có:
`1-1/2+1/3-1/4+...+1/49-1/50`
`=(1+1/3+1/4+...+1/49)-(1/2+1/4+...+1/50)`
`=(1+1/2+1/3+...+1/50)-2(1/2+1/4+...+1/50)`
`=(1+1/2+1/3+...+1/50)-2(1/2+1/4+...+1/50)`
`=(1+1/2+1/3+...+1/50)-(1/2+1/4+...+1/25)`
`=1/26+1/27+1/28+...+1/50`
`=>1/26+1/27+1/28+...+1/50=1-1/2+1/3-1/4+...+1/49-1/50`
Vậy `1/26+1/27+1/28+...+1/50=1-1/2+1/3-1/4+...+1/49-1/50`