Đáp án:
._.
Giải thích các bước giải:
Bài `2.2:`
`B=1/2-1/2^2+1/2^3-1/2^4+...+1/2^99-1/2^100`
`2B=1-1/2+1/2^2-1/2^3+...+1/2^98-1/2^99`
`2B+B=(1-1/2+1/2^2-1/2^3+...+1/2^98-1/2^99)+(1/2-1/2^2+1/2^3-1/2^4+...+1/2^99-1/2^100)`
`3B=1-1/2^100`
`-> B=(1-1/2^100)/3`
`-----`
Bài `2.3:`
`C=1/2+1/2^3+1/2^5+...+1/2^99`
`2^2 C=4C=2+1/2+1/2^3+...+1/2^97`
`4C-C=(2+1/2+1/2^3+...+1/2^97)-1/2+1/2^3+1/2^5+...+1/2^99)`
`3C=2-1/2^99`
`-> C=(2-1/2^99)/3`
`-----`
Bài `2.4:`
`D=1/2-1/2^4+1/2^7-1/2^10+...-1/2^58`
`2^3 D=8D=4-1/2+1/2^4-1/2^7+...-1/2^55`
`8D+D=(4-1/2+1/2^4-1/2^7+...-1/2^55)+(1/2-1/2^4+1/2^7-1/2^10+...-1/2^58)`
`9D=4-1/2^58`
`-> D=(4-1/2^58)/9`
