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. $\frac{260}{783}$
A= $\frac{260}{87}$