Đáp án+Giải thích các bước giải:
`b)D=1/(2*3)+1/(3*4)+1/(4*5)+....+1/(2015*2016)`
`=(3-2)/(2*3)+(4-3)/(3*4)+(5-4)/(4*5)+....+(2016-2015)/(2015*2016)`
`=1/2-1/3+1/3-1/4+1/4-1/5+....+1/2015-1/2016`
`=1/2-1/2016`
`=1008/2016-1/2016`
`=1007/2016`
`c)E=1/3-3/4+3/5+2/2015-1/36+1/15-2/9`
`=(1/3+3/5+1/15)-(3/4+1/36+2/9)+2/2015`
`=(5/15+9/15+1/15)-(27/36+1/36+8/36)+2/2015`
`=15/15-36/36+2/2015`
`=1-1+2/2015`
`=2/2015`
