Cứu e với, em cần gấp

`a)A=(1/2-1)(1/3-1)*....*(1/2022-1)(1/2023-1)`

`A=(-1)/2*(-2)/3*(-3)/4*....*(-2021)/2022*(-2022)/2023`

`A=1/2*2/3*3/4*....*2022/2023`

`A=(1*2*3*....*2022)/(2*3*4*....*2023)`

`A=1/2023`

`B=(-1)1/2*(-1)1/3*.....*(-1)1/2024*(-1)1/2025`

`B=(-3)/2*(-4)/3*....*(-2025)/2024*(-2026)/2025`

`B=3/2*4/3*....*2025/2024*2026/2025`

`B=(3*4*....*2025*2026)/(2*3*...*2024*2025)`

`B=2026/2`

`B=1013`

`D=1/(1*3)-1/(2*4)+1/(3*5)-1/(4*6)+....+1/(97*99)-1/(98*100)`

`D=(1/(1*3)+1/(3*5)+...+1/(97*99))-(1/(2*4)+1/(4*6)+1/(6*8)+....+1/(98*100))`

`2D=(2/(1*3)+2/(3*5)+....+2/(97*99))-(2/(2*4)+2/(4*6)+2/(6*8)+....+2/(98*100))`

`2D=(1/1-1/3+1/3-1/5+.....+1/97-1/99)-(1/2-1/4+1/4-1/6+....+1/98-1/100)`

`2D=(1-1/99)-(1/2-1/100)`

`2D=98/99-49/100`

`2D=4949/900`

`D=4949/1800`

`Vậy    D=4949/1800`