Đáp án:
(9/10 - 11/15) + (13/21 - 15/28) + 17/36 – 19/45... + (197/4851 - 199/4950)
Ta thấy :
(9/10 - 11/15) = 1/6 = 1/(2x3) = 1/2 – 1/3
(13/21 – 15/28) = 1/12 = 1/(3x4) = 1/3 – 1/4
(17/36 – 19/45) = 1/20 = 1/(4x5) = 1/4 – 1/50
(197/4851 – 199/4950) = 1/2450 = 1/(49x50) = 1/49 – 1/50
Ta được:
9/10 - 11/15 + 13/21 - 15/28 + 17/36 – 19/45... + 197/4851 - 199/4950 =
1/2-1/3+1/3-1/4+1/4-1/5+ …. + 1/49-1/50 = 1/2 – 1/50 = 24/50
Vậy :
A = 38/25 + 24/50 = 2
A = 2
chúc bạn học tốt
