1/2 + 1/14 + 1/35 + 1/65 + 1/104 + 1/152 = 12/19 nhé bạn !
Đặt S = tổng trên
2S=1/4+1/28+1/70+1/130+1/208+1/304
2S=1/1.4+1/4.7+1/7.10+1/10.13+1/13.16+1/16.19
2S=1/3.(3/1.4+3/4.7+3/7.10+3/10.13+3/13.16+3/16.19)
2S=1/3.(1-1/19)
2S=1/3.18/19
2S=6/19
S=6/19:2
S=3/19