`=1+1/3+1/5+...+1/97+1/99`
Số hạng tử của phân số là: `(99-1):2+1=50`
`=>` Tử số có `50` phân số.
Ta có:
`=(1+1/99)+(1/3+1/97)+...+(1/49+1/51)`
`=(99/99+1/99)+(97/3xx97+3/3xx97)+...+(51/49xx51+49/49xx51)`
`=100/1xx99+100/3xx97+...+100/49xx51`
Xét mẫu số:
`=1/1xx99+1/3xx97+1/5xx95+...+1/97xx3+1/99xx1`
`=(1/1xx99+1/99xx1)+(1/3xx97+1/97xx3)+...+(1/49xx51+1/51xx49)`
`=2xx1/1xx99+2xx1/3xx97x+...+2xx1/49xx51`
`=2xx(1/1xx99+1/3xx97+...+1/49xx51)`
Ta có:
`100xx(1/1xx99+1/3xx97+...+1/49xx51):2xx(1/1xx99+1/3xx97+...+1/49xx51)`
`=>A=100/2=50`
Vậy `A=50`
