Đáp án:
Giải thích các bước giải:
A= $\frac{36}{1.3.5}$ + $\frac{36}{3.5.7}$ +...+ $\frac{36}{25.27.29}$
A = 9 ( $\frac{4}{1.3.5}$ + $\frac{4}{3.5.7}$ +...+ $\frac{4}{25.27.29}$ )
A = 9 ( $\frac{1}{1.3}$ - $\frac{1}{3.5}$ +$\frac{1}{3.5}$ - $\frac{1}{5.7}$ +... +$\frac{1}{25.27}$ - $\frac{1}{27.29}$ )
A= 9 ( $\frac{1}{1.3}$ - $\frac{1}{27.29}$ )
A= 9 ( $\frac{1}{3}$ - $\frac{1}{783}$ )
A= 9( $\frac{261}{783}$ - $\frac{1}{783}$ )
A= 9 . $\frac{260}{783}$ = $\frac{260}{87}$