Đáp án:
Giải thích các bước giải:
`A=3/2-6/8+11/28-17/70`
`=>A=3/1.2-6/2.4+11/4.7-17/7.10`
`=>A=(1+1/2)-(1/2+1/4)+(1/4+1/7)-(1/7-1/10)`
`=>A=1-1/10`
`=>A=9/10`
Vậy `A=9/10`.
Đề sai.
`B=4/3-8/15+12/35-16/63+20/99-24/143+28/168-32/195`
`=>B=4/1.3-8/3.5+12/5.7-16/7.9+20/9.11-24/11.13+1/390`
`=>B=(1+1/3)-(1/3+1/5)+(1/5+1/7)-(1/7+1/9)+(1/9+1/11)-(1/11+1/13)+1/390`
`=>B=1-1/13+1/390`
`=>B=12/13+1/390`
`=>B=361/390`
Đề đúng.
`B=4/3-8/15+12/35-16/63+20/99-24/143+28/195-32/255`
`=>B=4/1.3-8/3.5+12/5.7-16/7.9+20/9.11-24/11.13+28/13.15-32/15.17`
`=>B=(1+1/3)-(1/3+1/5)+(1/5+1/7)-(1/7-1/9)+(1/9+1/11)-(1/11+1/13)+(1/13+1/15)-(1/15-1/17)`
`=>B=1-1/17`
`=>B=16/17`
Vậy \(\left\{ \begin{array}{l}B=\dfrac{361}{390}\\B=\dfrac{16}{17}\end{array} \right.\)
`C=6/5-14/45+22/117-30/221`
`=>C=6/1.5-14/5.9+22/9.13-30/13.17`
`=>C=(1+1/5)-(1/5+1/9)+(1/9+1/13)-(1/13+1/17)`
`=>C=1-1/17`
`=>C=16/17`
Vậy `C=16/17`.
