Đáp án:song roi
Giải thích các bước giải:
B=36/1.3.5 + 36/3.5.7 + 36/5.7.9 +.....+ 36/25.27.29
B/9 = 4/1.3.5 + 4/3.5.7 +.....+ 4/25.27
29
B/9 = 1/1.3 - 1/3.5 + 1/3.5 - 1/5.7 +
......+ 1/25.27 - 1/27.29
B/9 = 1/3 - 1/27.29
B = 3 - 1/3.29
B = 261/87 - 1/87
B = 260/87