Đáp án:
B= $\frac{36}{1.3.5}$ + $\frac{36}{3.5.7}$ + ... + $\frac{36}{25.27.29}$
B= 9 ( $\frac{4}{1.3.5}$ + $\frac{4}{3.5.7}$ + ... + $\frac{4}{25.27.29}$ )
B= 9 ( $\frac{1}{1.3}$ - $\frac{1}{3.5}$ + $\frac{1}{3.5}$ - $\frac{1}{5.7}$ + ... + $\frac{1}{25.27}$ - $\frac{1}{27.29}$ )
B= 9 ( $\frac{1}{1.3}$ - $\frac{1}{183}$ )
B= 9 . $\frac{260}{783}$
B= $\frac{260}{87}$
Vậy B = $\frac{260}{87}$
chúc bạn học tốt ^^