2 câu trả lời
~ Bạn tham khảo ~
3/[3*5] + 3/[5*7] + 3/[7*9] + ... + 3/[99*101]
= 3/2*(2/[3*5] + 2/[5*7] + 2/[7*9] + ... + 2/[99*101])
= 3/2*(1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + ... + 1/99 - 1/101)
= 3/2*(1/3 - 1/101)
= 3/2*98/303
= 49/101
//3/((3.5) +3/(5.7) + 3/(7.9) + ... + 3/(99.101)
=3/2.(1/3 - 1/5 + 1/5 - 1/7 + 1/7 - 1/9 + ... + 1/99 - 1/101)
=3/2.(1/3 - 1/101)
= 49/101
