Đáp án:
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 + 4/5.7.9 + .............. + 4/25.27.29 )
B = 9 ( 1/1.3 - 1/3.5 + 1/3.5 - 1/5.7 + 1/5.7 - 1/7.9 + .............. + 1/25.27 - 1/27.29 )
B = 9 ( 1/1.3 - 1/27.29 )
B = 2,9