Đáp án:
`B = 3/2 - 5/6 + 7/12 - 9/20 + 11/30 - 13/42 + 15/56 -17/72`
`B = 3/(1.2) - 5/(2.3) + 7/(3.4) - 9/(4 . 5) + 11/(5.6) - 13/(6.7) + 15/(7.8) - 17/(8.9)`
`B = 3 - 3/2 -5/2 -(- 5/3) + 7/3 - 7/4 - 9/4 -(- 9/5) + 11/5 - 11/6 - 13/6 -(- 13/7) + 15/7 - 15/8-17/8 -(-17/9)`
`B = 3 - 3/2 -5/2 + 5/3 + 7/3 - 7/4 - 9/4 + 9/5 + 11/5 - 11/6 - 13/6 + 13/7 + 15/7 - 15/8 - 17/8+17/9`
`B = 3 + (-3/2 - 5/2) + (5/3 + 7/3) + (-7/4 - 9/4) + (9/5 + 11/5) + (-11/6 - 13/6) +( 13/7 + 15/7) +(- 15/8-17/8) + 17/9`
`B = 3 + (-4) + 4 + (-4) + 4 + (-4) + 4 + (-4) + 17/9`
`B = 3 + [(-4) + 4] +[ (-4) + 4] +[ (-4) + 4] + (-4) + 17/9`
`B = 3 + 0 + 0 + 0 + (-4) + 17/9`
`B = 3 - 4 + 17/9`
`B = -1 + 17/9`
`B = -9/9 + 17/9`
`B = 8/9`
