A = $\frac{1}{3.5}$ + $\frac{1}{5.7}$ + $\frac{1}{7.9}$ + … + $\frac{1}{97.99}$ 

Đáp án:

Giải thích các bước giải:

 $A=\dfrac{1}{3.5}+\dfrac{1}{5.7}+\dfrac{1}{7.9}+…+\dfrac{1}{97.99}$

$ $

$=\dfrac{1}{2}.(\dfrac{2}{3.5}+\dfrac{2}{5.7}+…+\dfrac{2}{97.99}$

$ $

$=\dfrac{1}{2}.(\dfrac{1}{3}-\dfrac{1}{5}+\dfrac{1}{5}-\dfrac{1}{7}+…+\dfrac{1}{97}-\dfrac{1}{99})$

$ $

$=\dfrac{1}{2}.\dfrac{32}{99}$

$ $

$=\dfrac{16}{99}$